Deep in the greens of Narino province in Colombia, 20km from Pasto (yet feeling like much further as it is over a mountain) lies the 20x5km Laguna de la Cocha. A 'cocha' is a lagoon in Quechua, one of the main dialects of the region, and the it is also known as Guamues Lake. At the mouth of Rio Encano, Las Cochas, the main town, straddles the river and a canal as it empties into lake. It is a pretty village with cabins and parillas (grills) serving cuy (guinea pig) and trout, with a delicious desert of cheese and jam (dulce de mora). The peace, quiet, provinciality, green and mistyness give it an almost swiss-chalet feeling and its "ramshakle buildings" are a picturesque step away from bustling, grungy Pasto.
Perusing the sweets, hats and other crafts, mingling with other visitors from Ecuador and Colombia and wandering along the canals crossing the rickety bridges makes for a pleasant few hours.
In addition, there is a short boat ride across the lake to Isla Corota (and the Santuario de Flora y Fauna, a national park, though in poor repair as we were not allowed to go around the island due to erosion of the path). At an altitude of 2830m, it is a well-preserved evergreen cloud forest with an unusual small chapel research station and 550m long boardwalk (closed June 2013) that leads to a mirador and excellent bird-watching.
One of the unique ecosystems in Colombia (of which there are many) is the cloud forest (where they recently "discovered" a new mammal, the Olinguito), and Isla Corota is a really accessible example.
Source: Lonely Planet Colombia 6th Edition Aug 2012