Surf - Nicaragua has a remarkable number of world class surf breaks such as Manzanillo, Colorado, Madera, and Popoyo all of which are frequently featured in magazines such as Surfer.
Nicaragua Surf Report - a great web site for surfers
Also:
Explore the beaches
Hike the volcanoes
Canopy tours (multi-stage jungle cable adventures)
Day sailing
Boat rentals
Scuba diving
Watch the sun set into the ocean from a beach front bar
Trips to colonial Granada
Fishing
Spear fishing
Tours to visit sea turtles
Relax by the pool and enjoy the simple-natural beauty
Enjoy a meal in one of the many excellent restaurants
Shop for your own real-estate in paradise (Bulldog Inn has a special arrangement with REMAX - San Juan del Sur)
El Jardin Restaurant (next door to the inn)
Other Restaurants in San Juan
Island Volcanos

Beaches:
Madera
Romanso
Marsella
Manzanillo
Colorado
Popoyo