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In a magnificent black-lava field, the cyan Blue Lagoon spa is fed water from the futuristic Svartsengi geothermal plant; with its silver towers, roiling clouds of steam, and people daubed in white silica mud, it's an otherworldly place. Those who say it’s too commercial and too crowded aren't wrong, but you’ll be missing something special if you don’t go. Pre-booking is essential.

The superheated water (70% sea water, 30% fresh water, at a perfect 38°C) is rich in blue-green algae, mineral salts and fine silica mud, which condition and exfoliate the skin – sounds like advertising speak, but you really do come out as soft as a baby’s bum. The water is hottest near the vents where it emerges, and the surface is several degrees warmer than the bottom.

The lagoon has been developed for visitors, with an enormous, modern complex of changing rooms, restaurants, a hotel, spa and a gift shop, and landscaped with hot-pots, steam rooms, a sauna, a bar (one drink included with each ticket) and a piping-hot waterfall that delivers a powerful hydraulic massage – like being pummelled by a troll. A VIP section has its own interior wading space, lounge and viewing platform. The luxurious Retreat Spa, the Moss Restaurant and the five-star Retreat Hotel have all recently opened in the complex.

Premium entry to the lagoon gets you an algae mask, slippers and a bathrobe to use while in the facility, a LAVA Restaurant reservation (dinner not included) and glass of sparkling wine during dinner.

Those who just want to take a look and a few snaps of the lagoon can use the free short pathway around the complex, which continues on to the Silica Hotel.

The complex is just off the road between Keflavík and Grindavík.