[Punker]

I live in Costa Rica.

Arenal is nothing spectacular. Tabacon is very nice, but expensive. If you are travelling with a bunch of 23 year olds, I'm guessing you'll probably be looking for good times and partying. I'd suggest spending some time at Jaco beach which is kind of a surf/party area for many young people.

If you're single and want some "companionship" I'd suggest visiting the famous Del Rey in downtown San Jose. Even if you don't want companionship, it's still quite a site to see.

The canopy tours ("zip lines") are much more impressive than the canopy walks. There's any number of excellent ones so I don't really have any particular recommendation.

I will make one other comment about "the entire country is about the size of West Virginia, so I'm assuming anything worth seeing is fairly accessible". The comment about the size is true, but the roads infrastructure is very poor and underdeveloped - don't assume that just because something is 100 miles away that you can drive there in just a couple of hours. You can get any place you want, but it may take you double the time you might expect.