The hook
A small green valley hidden in the middle of a black volcanic plain — waterfalls, basalt columns and moss packed into a space you could cross in ten minutes, invisible until you are standing at its edge.
01Why it's worth it
Gjáin sits in Þjórsárdalur, a broad valley of ash and lava in the southern highlands, and it makes no sense from a distance. The surrounding country is bare and grey. Then the ground opens and there is a pocket of intense green with the Rauðá river falling through it in a series of small waterfalls — Gjárfoss the largest — over stacked basalt columns and around mossy outcrops.
It is small, and that is the appeal rather than a limitation: you can walk the whole thing in under an hour and it feels like a set rather than a landscape, which is presumably why Game of Thrones filmed here. Nearby, Háifoss — one of Iceland's tallest waterfalls at 122 m — drops into a canyon a short drive further up the same track, and the reconstructed Viking-age farm at Stöng is a few minutes away.
The access is the filter, and it is real. The track in is rough gravel, badly rutted in places, and while people do reach it in two-wheel drive in good conditions, the rental agreements usually forbid it and the road is closed entirely outside summer. That difficulty is why a place this photogenic is still quiet.
02How to experience it
Combine it with Háifoss and Stöng as a half-day loop off Route 32, in a 4WD, between roughly June and September. Go early or late — the valley is small enough that a single tour group fills it. Wear boots; the paths are wet and the moss is fragile, so stay on them.
From the locals
The strongest signal is behavioural rather than descriptive. One traveller, in a thread about places that look nothing like their Instagram versions: "we went to Gjáin and were the only ones there for hours… it was truly magical, and we loved it so much we recently went back to Iceland solely to visit that same spot again."
Going back to a country for one small valley is about as clear as a recommendation gets. They were also honest about the caveat: on a June visit there were "about 6–8 people circling in and out," so the emptiness is a matter of season and hour rather than a guarantee.
In a separate thread on the best places anyone had ever travelled, another named the same cluster: "Háifoss, in Iceland — the most special place on earth to me. I also loved Gjáin, Gljúfrabúi and Jökulsárlón."