Costa Rica sorts its year into two seasons rather than four, split by a spine of volcanoes down the centre of the country. The dry season runs from December to April. Guanacaste in the northwest is the driest corner of all, gold and dusty by March, while the Pacific beaches and the Central Valley around San Jose stay bright and warm. From May the rains return as the green season, usually holding off until early afternoon, so mornings are often clear enough for a canopy walk before the clouds build over Arenal and Monteverde. September and October are the wettest months on the Pacific side. That same pair is the sweet spot on the Caribbean, where Tortuguero and Puerto Viejo see more sun than usual and calmer seas while the west coast is under water. Temperatures barely shift across the year here. What changes is the rain, the crowds and the price.

Costa Rica packs an outsized share of the planet's species into a small country, and some of the best sightings are tied to the calendar. Green turtles haul up to nest on the black sand at Tortuguero from July to October, with hatchlings scrambling for the surf into November. On the south Pacific coast around Uvita, humpback whales appear in two separate seasons, roughly July to October and again from December to March, one of the longest whale watching windows anywhere. Up in the cloud forest, the resplendent quetzal is easiest to find in its breeding months from February to June, when the males trail their long tail feathers around Monteverde and San Gerardo de Dota. Howler monkeys, sloths and toucans stay put all year, so there is no wrong month for the forest itself.

For a beach-first trip, the dry months from December to April are the safe bet. The Pacific sand at Manuel Antonio, Samara, and the Nicoya Peninsula bakes under near daily sun, forest trails stay firm underfoot, and the sea is calm enough for easy swimming. Surfers split the year the other way. Gentler, beginner-friendly waves roll in through the dry season, while the bigger swells arrive with the green season from May onward. The best time to visit Costa Rica's Pacific coast for dependable sun is January to March, before the heat peaks in April.

There is a strong case for travelling in the rain. From May to November the crowds thin out, room rates fall, and the country is at its greenest, with rivers running high enough for white water rafting near Turrialba and La Fortuna. The pattern is forgiving. Most days open sunny, the showers come in the late afternoon, and they tend to pass. September and October are the wettest and quietest months, and also the moment the Caribbean coast comes into its own. Coffee drinkers can time the Central Valley harvest, which runs from about November into February as the dry season begins.

Costa Rican festivals lean on faith, farming and a fondness for a parade. Semana Santa, the week before Easter in March or April, is the biggest of the year, when much of the country slows down and heads for the coast. In the dry season the oxcart drivers of San Antonio de Escazu hold their painted cart parade, a nod to the ox teams that once hauled coffee down to the ports. On 2 August, hundreds of thousands of pilgrims walk through the night to the basilica at Cartago for the Romeria, honouring the country's patron saint. Independence Day on 15 September fills the streets with lantern processions and a relay of runners carrying a freedom torch south from Guatemala. Over on the Caribbean, Limon holds its carnival in October.

Planning a trip around these events allows you to experience regional traditions alongside famous natural sites.