The main attraction of this national park is Mt. Chirripó, the highest mountain in Costa Rica and a mecca for both hikers and serious summiteers. It's a 48-km (30-mile) roundtrip hike, with an elevation gain of 2,100 m (6,890 feet) to reach the hostel, and another 340 m (1,000 feet) to reach the summit. You need to plan gear and food carefully, be very fit, and acclimatize before setting out. The roundtrip usually takes three days—one day to climb to the hostel, one day to explore the surrounding summits, and one day to descend.
With the number of hikers limited to 40 per day, it's becoming ever more difficult to hike here, since most advance reservations are quickly snapped up by local schools and organizations. Phone reservations are accepted, but only on the first Monday of May and November. Outside of national holiday weeks, there is always the possibility that spaces will be available to hikers who show up without reservations, because not all the spots are reserved. So
your best bet is to try your luck and check in between 6:30 to 4 at the San Gerardo de Rivas National Parks Service office the day before you want to hike. Entrance is on a first-come, first-served basis. The maximum stay at the hostel is three days, two nights. Admission to the park is $15 per day, plus $10 per day for lodging. Ask for trail maps at the office. Don't try to sneak in: a park ranger will stop you at a checkpoint on the trail and ask to see your reservation voucher.