DH and I went, with another couple, to CR 3 yrs. ago. We loved it and would return anytime. I planned the entire trip using VRBO (Vacation Rentals By Owner) website. We flew into Liberia, the northern airport. Roads are very small and poorly maintained by our standards. Rental cars are tiny. We got the biggest avail, and barely had room for 4 adults with luggage. We were there for 2 weeks, and would have stayed longer if we could have.
If you want an adventure, try the hanging bridges or zip lines. I am scared (an understatement!) of heights, but did them both and survived! Eat the local food, tasty and inexpensive. Take enough cash, as getting $$ from a money machine is difficult and time consuming. People are friendly and you can get by with a smattering of Spanish. What part of the country will you stay in? Any time for sight seeing? Have a memorable trip!!