Samara is a laid back town so there are'nt a lot of activities, unless you call lying on a beautiful beach an activity.
You can get surfing lessons at Jessee's Surf School, as well as hiring bodyboards. You can kayak out to the island in the bay.
Hotels in the area can arrange sportfishing trips, or you could contact Kingfisher which is based out of Playa Carrillo.
Bike Costa Rica (tel. 656-0120) has a fleet of Trek mountain bikes that rent for $4 per hour or $25 per day.
Intercultura Language School offer a range of courses and private lessons and can arrange for a home stay with a local family.
All of the hotels here can help you arrange any number of tour options, including horseback rides, boat trips, scuba diving, and snorkeling outings. Tío Tigre Tours (tel. 656-0098), is a good all-around local tour company.
The waterfall near Belen- about 15 mins drive- is small & beautiful and during dry season it's safe to swim in the river beneath.