Every trip to costa rica should include a relaxing time at the multiple hot springs in La Fortuna/Arenal area.
My favorites include
Baldi Hot Springs https://www.baldihotsprings.cr/ great with friends, has water slides, swim up bars. Lots of international guests.
Tabacon https://www.tabacon.com/ great for romantic time as a couple or group of couples. Little more expensive, but has a great buffet as well.
Another option is the Springs Resort and spa http://www.thespringscostarica.com/ great place for weddings, and options for large groups of friends and family to stay in multi bedroom accommodations.
Tom's Pura Vida experiences 