Lying within Kahurangi National Park, the Oparara Basin is a hidden valley concealing limestone arches and caves within a thick forest of massive, moss-laden trees. The valley's signature sight is the 200m-long, 37m-high Oparara Arch, spanning the picturesque Oparara River, tannin-stained a fetching shade of caramel, which wends alongside the easy walkway (45 minutes return). The main car park, a 25km drive northeast of Karamea (very rough and narrow in places) is the trailhead for walks of various lengths, and there are excellent information panels here, too.
At the cave mouth of the Oparara Arch walk, some trampers continue uphill for lofty views but it's steep and treacherous (especially after rain), so we advise against it.
The smaller but no less stunning Moria Gate Arch (43m long, 19m high) is reached via a simply divine forest loop walk (1½ hours), which also passes the Mirror Tarn (itself 15 minutes from the car park).
Just a 10-minute walk from the second car park are the Crazy Paving and Box Canyon Caves. Take your torch to enter a world of weird subterranean shapes and rare, leggy spiders. Spiders, caves, darkness…sound like fun?
Beyond this point are the superb Honeycomb Hill Caves and Arch, accessible only by guided tours (three-/five-/eight-hour tours $95/150/240) run by the Karamea Information & Resource Centre. Ask about other guided tours of the area, and also about transport for the Oparara Valley Track, a rewarding five-hour independent tramp through ancient forest, along the river, popping out at the Fenian Walk car park.
To drive to the valley from Karamea, travel 10km along the main road north and turn off at McCallum’s Mill Rd, where signposts will direct you a further 14km up and over into the valley along a road that is winding, gravel, rough in places and sometimes steep. Don't attempt it with a campervan.