You will miss allege crowds going here, we only saw one person whilst we were out in the cloud forest. I haven't been to monteverde cloud forest but have been told by numerous people that it is very crowded.
The cloud forest itself is beautiful and very atmospheric with the mist/cloud covering. Don't expect to see any animals though, and if you do see one it will be a bonus - we saw a deer and some insects. I wouldn't say you need a guide, we did it on our own.
The one thing I was a little disappointed with was I thought they could have had leaflets or a poster or two in the entrance bit describing and giving more information about cloud forests, but I guess that's what you get a guide for.
It's a $4 return minibus to Santa Elena which picks you up from your accommodation. There are certain times it picks you up and returns from the park. Wear wet weather gear and sturdy footwear as it is wet up there!
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