City guide
Reykjavík KEF: What to Do on a Layover
Hallgrímskirkja and hot dogs in 3 hours: the church, Bæjarins Beztu, volcanic landscape.
Getting from the airport
KEF to city center: 45 minutes by bus (Flybus). Trains run every 30 minutes. Service runs 05:00 to 23:00. Skip the taxi unless your connection is under 5 hours.
What to do in Reykjavík
The stops worth making: Blue Lagoon, Northern Lights, Golden Circle, Reykjavik harbour. Rated above 4.4: Hallgrimskirkja (4.6), Perlan (4.5), Skólavörðustígur Rainbow Street (4.6), Sun Voyager (4.5), Lava Show (4.8). You do not need the full tourist circuit. Pick two and commit.
Visa and entry
Reykjavík is visa-free for US passports. No application, no fee. The border process at KEF is standard. Budget 30 minutes.
How long do you need
The minimum useful layover is 6 hours. That gives you 45 minutes in each direction plus about 180 minutes on the ground. Up to 24 hours is a proper overnight.