Hi SuzA,
Well, for a combo of ecotourism & diving, CR ranks right up there. You should have a super time.
It's been a few years since I've been back, but my last trip report should still be reasonably accurate:
"Best & most convenient diving is on Gulf of Guanacaste Coast, off of Playa Hermosa. This is a 3 1/2 hour drive over bad road from San Jose (the capital) or a 40 minute plane ride into Liberia. Caribbean side of country has essentially no diving, although there some off Cano Island in the far SW.
Bill Beards (800-779-0055; billbeards@netrunner.net) does a great job at catering to all levels of divers. He was the granddaddy of recreational diving there & a great character, but he & Nadine have sold the op. New owners reportedly doing a great job, too. They have nice roomy boats, fun and helpful dive masters, and take care of your gear from arrival to departure -- excellent munchies and snorkeling opportunities during SI.
The conditions in this area vary wildly, often over a short period of time, particularly the viz. Also, this is eastern Pacific & not Caribbean diving, so don't expect colorful corals & sponges, lush reefs, water in the mid-80s & 100'+ viz. However, if you are happy with 15 (low end close to shore)-90 (high end out islands) foot visibility, warmish water, calm seas, nice beaches, friendly people, good food and reasonable prices, it's Kool. There is likelihood of seeing eagle rays, white tipped reef sharks, bulls sharks, & mobulae (small Pacific mantas). Occasional whale sharks. Topside, see the rain forest by aerial tram, drive through cloud forests to visit an active volcano, soak hot thermal springs and waterfalls, and raft the Rio Pacuare. Your hotel can handily arrange all of this.
'In shore' sites are 20 minute boat rides, while 'offshore' sites, "Bats and Cats" (Catalina Island is an hour away, and "The Bats" is a two hour ride away). The offshore sites are more expensive, however, the caliber of diving was better further off shore.
If you want isolation & really great wilderness activity, go south to the Osa Peninsula & dive Cano Island (similar to the "Cats & Bats" mentioned above). Go during dry season - January to September. Check out the La Paloma Resort (800-351-5041; fax 209-532-1979) for the experience of a lifetime -- its like living in the jungle.
It is a safe, varied country with much to see and do. People are friendly. A little Spanish helps but is not necessary."
Have a blast.
DocVikingo