Croatia's juxtaposition of crystalline waters and rugged mountains opens up a wealth of opportunities for the active traveller. The gorgeous coastline and myriad islands are a renowned boaties' playground, while in the interior, a network of hiking and biking trails gives access to forest-fringed lakes, verdant valleys and magnificent uplands.

Swimming

If there's just one activity you're planning to partake in during a Croatian holiday, we'd put money on it being this one. Croatia's clear waters are nigh on irresistible on a hot day, and the European Environment Agency rates 98% of Croatia's bathing sites as having excellent water quality. In summer the water temperature can reach over 25°C, and it's usually over 20°C from June right through to October.

There are good swimming spots along the entire coast and throughout the islands. Beaches come in a variety of textures: sandy, shingly, rocky. Some of the best – like blissful little Stiniva, on Vis, and Dubovica, on Hvar – have large smooth white pebbles. Locals tend to favour the pebbly beaches, partly because many of the sandy beaches are extremely shallow. This is especially true of those around Lopar on Rab, although less so for the sandy beaches at the eastern end of Vis and places like Prapratno on the Pelješac Peninsula.

In summer the Adriatic can more closely resemble a millpond than the sea, but the waves pick up when the wild wind known as the bora arrives in winter. During the peak season, however, conditions are generally safe and the main hazards are the sea urchins that reside in the rocky shallows. Many people wear plastic swimming shoes as a precaution.

Away from the coast, popular swimming spots include the lakes at Krka National Park, Zagreb's Jarun Lake, and the island of Ada, on the Danube, near Vukovar.

Hiking

Hiking in Croatia can be as untaxing as a slow stroll around the boardwalks and well-maintained lakeside trails of Plitvice or as challenging as an assault on the high reaches of Paklenica. Local tourist and national-park offices are well equipped to recommend a walk to suit your time constraints and level of ability. Many produce their own free walking maps or sell detailed maps for more remote areas. If you're contemplating a serious expedition, consider contacting the Croatian Mountaineering Association, which can provide information and access to a network of mountain huts, or joining a guided walk organised by one of the many agencies specialising in adventure tourism.

Spring, early summer and autumn are prime hiking times, beating the worst of both the crowds and the summer sun. The karstic coastal mountains roast in July and August, offering very little shade or water, while the leafy trails of Plitvice and Krka get clogged with people. In these months, try less-visited Risnjak National Park or head even further inland.

Žumberak Samoborsko Gorje Nature Park, near Samobor, offers the best hiking in Croatia's interior, featuring forests, caves, river canyons, waterfalls and nine mountain huts. Medvednica Nature Park, north of Zagreb, is also good.

In Istria, there are trails around Buzet and Poreč, and a well-marked 11.5km circular hiking track leading from Gračišće. The Kvarner region offers off-the-beaten-track hiking in both Učka Nature Park and Risnjak National Park. Risnjak's Leska Path is a recommended, easy 4.2km trail through the forest where you might even spot wildlife. The islands of Cres, Lošinj and Rab also have a wealth of good trails.

Dalmatia is spoilt for choice, but the most obvious hiking highlights are the national parks Plitvice, Krka and Paklenica, and Biokovo Nature Park. The first two offer plenty of easy lakeside strolls, although they do get insanely busy in summer. Paklenica and Biokovo are both mountainous terrains, offering superb views over the coast and islands. There are also brilliant walks on the islands of Brač, Hvar, Vis, Lastovo and Mljet, and in the mountains above Omiš and Orebić.

Cycling

Bicycle touring is increasingly popular in Croatia, both independently or with organised groups. Bike hire is easy to arrange and there are plenty of relatively quiet roads to explore, especially on the islands. Try to avoid the main Adriatic highway – there are no bike lanes, few passing spaces and it's extremely busy. Thankfully much of it can be bypassed by catching ferries; bikes can be taken on car ferries for an additional charge but not on catamarans.

March, April, September and October are the best cycling months, with mild, mostly dry weather. The traffic is much busier from June to August, and it can get extremely hot.

Slavonia has a couple of excellent long-distance trails: the 80km Pannonian Peace Route between Osijek and Sombor in Serbia, and the 138km Danube Route, tracing the Hungarian and Serbian border.

The best route, however, is the Parenzana Bike Trail, which follows a former railway line between the Italian city of Trieste and Poreč in Istria (the Croatian section is 78km long). Also in Istria, there are bike trails around Buzet, Pazin, Poreč and Rovinj, and an unchallenging 60km cycling trail winding around the coast from Pula to Medulin.

Kvarner is another great region for cyclists, with 19 routes around Opatija, Učka Nature Park and the islands of Cres, Lošinj, Krk and Rab detailed in the Kvarner by Bicycle brochure, available from local tourist offices.

In Dalmatia, there are scenic cycling trails on the islands of Mljet and Lastovo. The Central Dalmatia Bike brochure details six routes on the Makarska Riviera, ranging from an easy 15km ride around Makarska to a gruelling 61km climb up Biokovo to a height of 1749m. Biokovo is also good for mountain bikers, as are the islands of Korčula and Brač, where trails lead to the island's highest point, Vidova Gora (778m).

Useful websites with information for cyclists include www.pedala.hr (in Croatian) and www.istria-bike.com.

Diving & Snorkelling

The most striking thing about the Adriatic coast is the clarity of the water. Snorkelling is worthwhile pretty much everywhere, although there are some extraspecial spots, such as Crveni Otok near Rovinj.

The area's turbulent history has also bequeathed it with numerous interesting underwater sights, from wrecks dating to antiquity through to a downed WWII plane. The latter is off the coast of Vis, where there's also an amphorae field and shipwrecks to explore – although the most interesting sites here are at depths that require technical diving skills.

Other famous wrecks include the Taranto, an 1899 Italian merchant ship sunk by a WWII mine off Dubrovnik; a 3rd-century Roman ship and a German WWII torpedo boat off the island of Mljet; the Rosa, off Rab; the Peltastis, a 60m Greek cargo ship, off Krk; and the Baron Gautsch, an Austrian passenger steamer sunk by a mine near Rovinj during WWI.

On top of that there are plenty of reefs, drop-offs and caves to investigate. Marine life includes scorpionfish, conger eels, sea snails, sea slugs, octopuses, lobsters, the rare giant mussel, red coral, red gorgonian fans and colourful sponges.

There are diving centres all along the coast, with particular hot spots being Poreč, Rovinj, Pula and the Brijuni Islands in Istria; the islands of Krk, Cres, Lošinj and Rab in the Kvarner area; the Dalmatian islands of Dugi Otok, Brač, Hvar, Vis and Mljet; and Dubrovnik.

For further information, refer to the Croatian-only website of the Croatian Diving Association (www.diving-hrs.hr).

Sailing

Could there be a more blissful holiday than gliding between remote islets and otherwise-hard-to-access beaches all day, before finding a pretty spot to moor for the night?

Sailing was once the exclusive preserve of the rich, but Croatia now offers plenty of more affordable opportunities for both day sails and organised multiday tours. Operators such as Sail Croatia even target cruises to young backpacker types.

If you'd prefer to go it alone, it's an easy matter to charter a boat, either with a skipper or, if you're suitably experienced, on a 'bareboat' basis. Useful contacts include the Adriatic Croatia International Club (www.aci-marinas.com), which manages 22 marinas, and the following charter companies: Cosmos Yachting, Nautika Centar Nava, Sunsail, Ultra Sailing, Yacht Rent and Yacht Charter Croatia (www.croatiacharter.com).

Kayaking

Kayaking, of both the sea and the river varieties, is a popular activity in Croatia. Kayaks can be hired from numerous locations, and there are many specialist operators offering both short paddles and multiday island-hopping expeditions.

It's particularly popular in Dubrovnik, where you'll see great shoals of kayakers heading out on guided trips – with sunset paddles being especially well subscribed. There are also good crews operating out of Split, Cape Kamenjak, Rovinj, Poreč and the islands of Korčula, Vis, Hvar and Rab.

Inland, don't miss the opportunity to kayak on the Danube at Vukovar and on Zagreb's Jarun Lake.

Windsurfing

Croatia's two prime windsurfing locations are Bol on the island of Brač and Viganj, near Orebić on the Pelješac Peninsula. Both are exposed to the maestral, a strong constant westerly that generally blows from morning to early afternoon from April to October. The optimum conditions tend to be at the end of May/early June and the end of July/early August.

Other good spots include Makarska, Mali Lošinj, Cape Kamenjak and Poreč, and you can even windsurf inland on Zagreb's Jarun Lake. At all of these locales you can hire boards and take lessons.

Rock Climbing

Croatia's best rock climbing is in Paklenica National Park, with graded climbs for all levels of ability including 72 short sports routes and 250 longer routes. A rescue service is also available. Sticking in Dalmatia, there are climbing crags on Marjan Hill, right in the centre of Split.

Heading up the coast, there are a couple of sites near Baška on Krk Island. The best climbing in Istria is in a defunct Venetian stone quarry near Rovinj, which has 80 climbing routes. Free climbing is also possible near Buzet and Pazin.

There's also a famous rock-climbing area in the Plešivica section of the Žumberak Samoborsko Gorje range, west of Zagreb.

March, April and May are the best months for climbing, before the summer heat kicks in. The wind tends to pick up in autumn and winter.

The easiest way to get started is to enquire at local tourist offices or to contact one of the local agencies specialising in adventure tourism. The Croatian Mountaineering Association also has some information on its website (in Croatian).

Rafting

Croatia's prime rafting locale is the Cetina River, which spills through a steep gorge and into the Adriatic at Omiš. It's an easy matter to join a trip in the pretty little town, as operators tout for business by the riverside. Otherwise, specialist adventure agencies in Split and Makarska organise transfers and expeditions with reputable rafting companies.

Trips are possible from around April to October, with the fastest flows in April and after heavy rains. In summer it's a more gentle experience, of more interest to first-timers.

Skiing

Only 20 minutes from Zagreb, the Sljeme Ski Resort has lifts heading up to five downhill runs on the side of Mt Medvednica. The best snow cover is in February, but the season can stretch for three to four months with the use of snowmaking equipment. Night skiing is also possible.

Wildlife Watching

Croatia's premier wildlife-watching spot is Kopački Rit Nature Park in Slavonia, a significant wetlands on the flood plain of the rivers Danube and Drava. Nearly 300 species of bird have been spotted here, including white-tailed and imperial eagles, black storks, great crested grebes, purple herons, spoonbills, wild geese and woodpeckers. They're joined by 44 species of fish and 21 different kinds of mosquito (bring repellent). If you're extremely lucky, you might spot some of its mammalian inhabitants, such as red deer, wild boar, beavers, pine martens and foxes. The best time for spotting birdlife is during the spring (March to May) and autumn (September to November) migrations.

The Kvarner region is also rich in wildlife. The mighty griffon vulture roosts on the islands of Cres, Krk and Prvić, while Lošinj has centres devoted to the preservation of sea turtles and dolphins. Risnjak National Park is named after the lynx, which lives in the virgin forest here alongside brown bears, wolves, chamois and wild boar. You're unlikely to see these superstars of the forest, but you might spot deer at feeding stations along the tracks and you're bound to see some of the 500 species of butterfly. The Učka Nature Park also has brown bears, wild boar, roe deer and golden eagles.

Despite the summertime hordes, Plitvice Lakes National Park hides bears, wolves, deer and boar, alongside rabbits, foxes and badgers. If you can divert your gaze from the waterfalls, you might spot hawks, owls, cuckoos, kingfishers, wild ducks, herons, black storks and ospreys.

In Dalmatia, Paklenica National Park is home to various birds of prey, while Krka National Park has eagles and migratory marsh birds.