My brother in law is from Costa Rica and my sister lived there for a few years. Here is what she sends to people whenever they ask about a CR trip:
https://www.anywhere.com/costa-rica
Anywhere Costa Rica webpage is a great resource for planning a trip to Costa Rica. It breaks down the country by type of destinations and best places to stay and visit depending on what type of vacation you’re look to have.
The best beaches in Costa Rica are definitely in Guanacaste (North West part of Country). Tamarindo is probably the most popular beach town in Guanacaste for tourist and has lots of different hotels. Playa Conchal has the Westin Golf Resort and Spa which I hear is beautiful but VERY expensive.
This page breaks down all the towns in Guanacaste and is very informative.
https://www.anywhere.com/costa-rica/regions/guanacaste
If you plan on staying in the northern part of the country, it is easier to fly out of Liberia International Airport as opposed to San Jose.
If you are looking to fly into San Jose and want closer beaches, the pacific coast beaches are also beautiful. Manuel Antonio is one of the most popular tourist destinations. Also, Los Suenos Resort has a marina, Marriott hotel, and golf course if you’re looking for a resort experience.
Jaco is a beach town that is known for its crazy night life, definitely a party city which means more filth and creeps. Not the best beach either.
Dominical on the pacific coast is a clean, nice beach.
If you are looking for a Mountain, Cloud Forest experience, Monte Verde is beautiful and a great place for hiking.
Arenal Volcano – Another big tourist location. Beautiful volcano, hikes, hot springs, and spas.
On the Caribbean Coast Totuguero is an awesome experience. It is a nesting beach for turtles, so they have guided night tours to watch turtles lay eggs or watch eggs hatching. Good kayaking, hiking, fishing.
If you really want an off the beaten path experience, contact me and I will set you up with my friend Fabian, who has a tourist center in the town where I lived in the Mountains outside of Turrialba. The best white water rafting river (Pacuare) can be accessed from Turrialba.