I did this last September with two good friends and loved it. We hired a sherpa and donkey to carry our stuff up for us - no need to try and be a tough guy on this trip, it's such an opportunity it is best to enjoy it. We hiked up with just day packs with some extra clothes and snacks, and of course water. It's a beautiful hike as you go from below the clouds to the cloud forest to above the timber line. We made it up to base camp in about 7.5 hours, made a delicious meal, and then slept. Sleeping was really hard the first night due to the altitude, but we got over it. The next morning you get up early and climb to the peak of Chirripo, obviously best to do it to see the sun rise. It's absolutely stunning. After climbing to the summit you can hike all the way back down and leave, but we stayed the night to enjoy it. I'd definitely recommend buying small propane heaters to cook a warm meal, it will taste delicious after that hike!
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