What kind of soak do you want?
Natural hot springs — safety
Iceland's natural hot springs look magical but most are unmanaged: no temperature control, no change rooms, slippery rocks, occasionally boiling water near the source. Landmannalaugar's hot spring has a strict 5-minute soak limit because of bacterial content. The "free" springs closer to Reykjavík (e.g., Reykjadalur) are safer but require a 7 km round-trip hike.
Bring water (you'll dehydrate), change clothes before hiking back, and never enter with open wounds — the geothermal bacteria can cause nasty infections. If your eyes sting, you've been in too long.
FAQ
Is swimming in Iceland a "must"?
Yes, but municipal pools, not the expensive lagoons. The Reykjavík city pool system (Sundhöllin, Vesturbæjarlaug, etc.) is cheap (~ISK 1,300), authentic, and where locals actually go. See Tool #27 for the etiquette.
Is Blue Lagoon worth it?
It's polished, photogenic, and expensive. If you want the iconic milky-blue photos, yes. If you want value and authenticity, no. The Sky Lagoon (Reykjavík) and Mývatn Nature Baths (north) are cheaper alternatives with similar beauty.
Can I bring food / alcohol?
At natural springs, yes (no glass). At municipal pools, food is restricted to the cafeteria. At lagoons, only food bought on-site. Don't bring alcohol to any pool — it's the fastest way to be asked to leave.