Costa Rica travel advice

[DoctorJ]

After a long, cold stretch of winter last year, my wife and I decided to go someplace warm this February, so we're thinking about spending a week in Costa Rica.

Any advice? We're probably out of shape for major hiking and such, but we would like to see some nature. We'd like to spend a couple of days at the beach, and some rafting would be nice. We very much prefer "fun and quirky" to "nice".

Here's the big question--should we plan out the whole week in advance, or plan out the first couple of days and figure out the rest as we go? On the one hand, I hate to lock ourselves in, the idea of going where we like is appealing, and we want a little adventure. On the other hand, it's kind of high season when we'll be there, and we're a little long in the tooth to spend the night in a bus station. The third option is to go with a full-bore tour company, but that just seems like wimping out.

Thoughts?