San Carlos is a small town at the foot of the great lake, where it empties its waters into the San Juan river, its only outlet to the ocean. On a hill behind the town, and commanding the entrance to the river, are the ruins of a once strong fort built by the Spaniards, the crumbling walls now green with the delicate fronds of a maiden hair fern (Adiantum). The little town consists of a single rugged street leading up from the lake. The houses are mostly palm-thatched huts, with the bare earth floors seldom or never swept. The people are of mixed origin, Indian, Spanish, and Negro, the Indian element predominating. Two or three better built stores, and the quarters of the military governor, redeem the place from an appearance of utter squalor. Behind the town there are a few small clearings in the forest, where maize is grown. Some orange, banana, and plantain trees exhaust the list of the productions of San Carlos, which is supported by being a calling place for all vessels proceeding up and down the river, and by the Ulleros or rubber-men who start from it for expeditions up the Rio Frio and other rivers. We found there two men who had just been brought down the Rio Frio by their companions, greatly injured, by the lianas up which they had made their ladder to ascend one of the rubber trees, having broken and precipitated them to the ground. I learnt that this was a very unusual accident, the lianas generally being very tough and strong, like great cables. Most fabulous stories have been told about the Rio Frio and its inhabitants; stories of great cities, golden ornaments, and light-haired people, and it may be useful to relate what is known about it.