If you are looking for girls, the closest action place is Jaco - its on the coast; closest beach to SJ - its about 2 hrs, and the bus is very cheap - may be worth a night to say you saw it - be warned; Jaco is hot, and a dirty town; better beaches exist too - and the "action" is more abundant in San Jose.
If you are looking for a more traditiional tour, to see waterfalls, etc, as well as some of the country, the always popular "5 in one" or "4 in one" tours may be good - your hotel can help you - there is all zip lining - a couple of years ago, I did a zip tour outside of Cartago - the one in Jaco was better (and the one in Monteverde was better still) but you can check these out when you are down, or do a search for more info. A lot depends on you, and what you are seeking, as well as how long you are in CR - for a long weekend, for example, I'd stay in San Jose.
While I'm on the subject of tours, don't ignore the possibility of a tour offered by CTR member Bilko - you can PM him - another member, Pops, also gave great tours, but reports are he is still on the mend after suffering a bad traffic accident, so I don't know his avalibility, but again, you could PM him for more info - I personally know both guys; you could not go wrong with either
