For most travellers, yes — it is worth it. Sky Lagoon gives you Iceland's geothermal bathing culture without leaving the city for half a day: a warm oceanfront lagoon, a dramatic infinity edge, and a structured bathing ritual, set on the cliffs of Kársnes Harbour in Kópavogur. It is a modern, purpose-built spa rather than a wild hot spring — and that is its strength, because it is convenient, calm, and easy to slot into a Reykjavík trip.
The setting is the reason to come. The roughly 70-metre infinity edge appears to pour straight into the Atlantic, with views toward the Reykjanes Peninsula and, on clear days, the Snæfellsjökull glacier. In winter you may catch the Northern Lights from the warm water; in summer, soft midnight-sun light lingers over the ocean. If you only have time for one of Iceland's big lagoons and want calm and convenience, make it this one.