This is the best that Costa Rica has to offer: 8 nights (or more) in total with 1 night San Jose, 2 nights Manuel Antonio beach on the Pacific with a sail/snorkel tour included, 2 nights Arenal Volcano with hot springs and volcano viewing. Then do a river rafting trip on the Pacuare river, view unspoilt nature while navigating exciting class III-IV rapids. Then 2 or more nights in Puerto Viejo enjoying the beaches of the Caribbean and 1 more final night in San Jose. Prices include all taxes and round-trip transport from San Jose.
You can also add Monteverde and/or Tortuguero to this trip. Or use this as a base itinerary and customize it to make it completely your own!