Way down the Chiquibul Road in the Mountain Pine Ridge area, halfway to Caracol, is the forest research village of Douglas de Silva. Signs point the way to Rio Frio Cave, which lies about a mile from the village On the way to the cave you pass a sign for Twin Cave and Nature Trail. Continue ahead to the parking lot. Walk a minute down the paved path until your jaw drops to the ground; that's how you know you've arrived.
The massive, yawning entrance to the Rio Frio cave is overwhelming. A trail leads up the slope and into the cave's mouth, where you can clamber around in its massive chamber, which is well-lit by sunlight. A large pool of water covers most of the giant chamber.
Continuing down the path you'll see the other entrance to the cave on the far side of the mountain. Basically, the Rio Frio formed this cave as a shortcut instead of having to wind around the ridge. Damn lazy river!
Unless you have climbing equipment or want to swim, you can't walk into one entrance and out the other. To visit the far entrance, you'll need to take the Twin Cave Nature Trail you passed on the way in.
A flashlight is helpful here but not necessary. There's no entrance fee and no need for a guide. Rio Frio Cave is one of the few caves in Belize that you are welcome to explore on your own.
If you don't have a vehicle to get down here, you can book a Mountain Pine Ridge tour from San Ignacio. For around $30 you'll spend the afternoon exploring Rio Frio Cave and swimming in the waterfalls of the Rio On. Most tours to Caracol also stop at Rio Frio Cave.