while i havent been there myself, way south on the pacific, is corcovado. its very remote, and people go there to get into nature. uvita is on the way, so youd have to stop in bitcoin country. corcovado is about as far south as you can go without getting into panama, so if that seems too out of the way for your trip, like i said, monteverde is a popular option for getting into the wild, and its near arenal volcano. note that there are two airports you can fly into, san jose and liberia. liberia is much smaller and frankly a better experience. consider that based on your specific plans.

another really cool remote option is the southern part of the nicoya peninsula, for example mal pais. montezuma is a cool nearby town too. samara and nosara are known for surfing, but if you are new to surfing youll probably want a calmer beach. in general its not hard to find surfing and horseback riding at beach towns.

if you decide to go down the pacific coast, dominical is a cool beach town, and a good place to try surfing. this is on the way to uvita (and corcovado). theres a waterfall called nauyaca nearby that is fun to hike to and swim in the pool (better for dry season probably). 

renting a car, and preferably a 4x4 if youre going remote, is the best option (not cheapest). it gives you the freedom to go where you want when you want. pretty much highly recommend this unless you plan to be in more major destonations where public transit is more available. driving is a little crazier than places like the usa, but doable.