Liberia International Airport is the closest to Tamarindo being around an hour away. However, flying into San Jose International Airport is usually half the price while being a four hour drive.
We would highly recommend renting a car as it is the most convenient option. There is an affordable bus system (Buses Alfaro) that can take you from San Jose to Tamarindo for $15. You will have to uber or use a taxi to get back and forth from the bus station. While in Tamarindo, uber and taxis are available for transportation.
La Baula: they serve amazing pizza. (TIP: get the hazelnut ice cream) Bamboo Sushi Pangas: this is a nice (more expensive) beachfront restaurant Agua Salada: some seafood options and traditional Costa Rican food--very good, but few options Seasons: fine dining Mediterranean fusion Papaya Verde: mellow restaurant with very good fish and shrimp tacos.
Horseback Riding: You can rent a couple horses and go horseback riding at the beach. Canopy Tours: There's a few canopy places around Tamarindo you can go to. Surf: There's many places that rent surfboards around Tamarindo Scuba Diving: If you're licensed, there's beautiful diving in the area.