Firefly Spa

Firefly Spa is built around contrast therapy — alternating heat and cold, specifically a stint in a commercial-grade infrared sauna followed by a plunge into a tub chilled to the high 50s — and it’s set up so you don’t need an appointment to do it. Walk in, use the open sauna and plunge tubs on your own schedule, or book the private “Oasis” room if you want the experience without an audience.

It’s popular with athletes and gym regulars managing soreness and inflammation, but the pitch works just as well for anyone whose job or life leaves them tense and under-recovered. First visits are free, which takes the pressure off deciding whether cold plunging is your thing before you’ve actually tried it, and monthly memberships bring the per-visit cost down if it turns into a habit.

On our radar for the recovery-and-biohacking crowd, or anyone who’s watched a cold plunge video and wondered if they could actually handle it — this is a lower-stakes way to find out than jumping into a lake in February.