It's true, October in Costa Rica is one of the last months of the country's rainy season (May to November). But it's also known as the "green" season because the nation's flora is in full bloom. There are demonstrable benefits to traveling during these months, a principal one being that you can enjoy cooler temperatures on your holiday. (More on traveling in the green season here.)
On the northern Pacific coast, for example, average temps in the green season are in the high '70s (as opposed to the '80s and '90s during the dry season). One region where it's actually considered the dry season during this time is the Caribbean coast. So if you visit here you'll likely get perfect beach weather, less rain, and temps in the mid-'70s to mid-'80s.
Crowds & Costs
During the green season, in popular areas like Manuel Antonio National Park, the Nicoya Peninsula, Arenal, and Monteverde, there are going to be fewer crowds. If you are the type of traveler who likes to avoid the tourist hordes, then this is definitely the time to visit. Even in these popular areas, you should be able to find hotel rooms at often steep discounts. Of course, the international flights here are going to be cheaper as well, and domestic flights are occasionally cheaper as well.
Where to Go
Pacific and Caribbean coasts are great spots to visit in October. The landscape of much of Guanacaste Province (read more here) on Costa Rica's northern Pacific coast, is tropical dry scrub. This dry weather here doesn't fluctuate much throughout the year, so you're mostly guaranteed sun. Of course, there will be more rain in places like the Nicoya Peninsula, but the tradeoff is if you travel during this time you can visit popular villages like Tamarindo without them being so overcrowded.
As mentioned, the Caribbean side is also ideal in October. Unlike most of the country, this region is experiencing its dry months during this time. So maybe plan a trip to Limón Province, on the southern Caribbean coast, and definitely visit idyllic little surf villages like Puerto Viejo (read more here). There's a fascinating Afro-Caribbean culture here that you won't find in other parts of the country. It's the perfect village in which to surf and relax to cool coastal vibes without a care in the world.
What to Do
With the drier northern Pacific coast still experiencing sun, you may want to consider a surf excursion down the famous Gold Coast (from the Nicoya Peninsula on down to Punta Arena Province). You can make a road trip out of it and hit popular surf villages like Tamarindo and Jacó. Sure, you might experience a rain-out or two, but just give it an hour or two and those afternoon showers will likely clear right up.
You can also head to the northern Caribbean coast, and Tortuguero National Park (read more here). October marks the last month of turtle nesting season on this stretch of coastline. So come and spot female leatherback, olive ridley, and green sea turtles storming the beach as the sun goes down to lay their eggs. It's an unforgettable sight.
Events in October
Caribbean Carnival. Every year starting on Columbus Day, Limón Province, including the surf town of Puerto Viejo, celebrates carnival. This raucous 12-day party is a celebration of Afro-Caribbean heritage that includes live music, street dancing, parades, and regional cuisine.
Traveling to Costa Rica in October? Check out these great itineraries.
Explore Guanacaste from Liberia. Take advantage of Guanacaste's good October weather with a five-day beach getaway. You'll have plenty of time to relax and soak up the unique landscapes and beaches of the region, with just the right amount of adventure thrown in.
Caribbean Coast Adventure. From rainforest hikes to snorkeling in coral reefs, this itinerary is ideal for travelers going to Costa Rica during the green season, as the Caribbean coast stays relatively dry during these rainy months. It's also the best time to see turtles nesting on the beaches in Tortuguero National Park (July-October).