In the morning, we visited the El Castillo's Butterfly Conservatory. It's close to La Fortuna. The place was huge, with wildlife and jungle trails, butterfly tents, frog tents, orchid gardens and hilltop vistas. It's a pleasant stop for a few hours if you like that sort of thing and with butterflies landing on you.
We then drove the windy road around the lake to Santa Elena, stopping along the way for wildlife sightings, gorgeous views and bakery shops.
Santa Elena is packed with tour companies offering the usual - zipling tours, quad biking, hot springs, national park tours, coffee and chocolate tours, etc, so it's a good base to book onto activities.