Amazonia is the rainforest region in the south of Colombia.
While short on movie theaters and golf courses, the Colombian Amazon has its fair share of possibilities for outdoor activities. Fishing is likely the regions favorite sport (but followed closely, of course, by football), with piranha fishing being especially popular with the visitors. Boating the rivers provides incredible opportunities for wildlife spotting: river dolphins, tapirs, caymans, golden eagles—with the immense biodiversity of the rainforest, you will hardly scratch the surface. It is quite worthwhile to do some trekking in the jungle as well. Although trekking is not as great for wildlife spotting, a good guide will help you identify the interesting flora and sounds of the jungle, and may be able to take you to a local village or a maloca. Swimming in the jungle is also a lot of good fun, although fears of the legendary candirú, caymans, snakes, piranhas, etc. do often dissuade the weak-kneed.
Most of the Colombian Amazon (including Leticia!) is so remote and isolated that food will have to be local, and thus having fewer and more expensive vegetables, less meat, and far less dairy. On the upside, this means that you will be eating lots of fresh food, like fish and fruit, and on the downside, you might wind up eating a certain amount of canned food as well. For fish, look out for local favorites like pirarucú and dorado. The former is leaner but delicious and the latter very fatty and rich. Piranha is another common local food, since the Amazon is really full of them. While too small to make for an easy meal, piranha meat is actually quite tasty.
It's hard as hell to find (it's a little more common in the Peruvian Amazon), but drink afficionados really should seek out chuchuhuasa, a spirit made from the bark of the eponymous plant mixed with aguardiente. Tasting much like a sweeter version of bourbon, the drink is more popular with locals inside the jungle, rather than in the towns, where it is generally not commercially available. It's actually pretty great for a jungle trek, as the plant contains a strong stimulant (and, reputedly, aphrodisiac) effect, in addition to conditional medicinal benefits, treating ailments such as diarrhoea, arthritis, menstrual irregularities, and upset stomach.
Yagé (pronounced yah-HEY, with a very soft h) is a drink, known better in other countries as ayahuasca, uniting virtually all the multitudinous and disparate indigenous cultures of Amazonia. A strong hallucinogen, its primary use is religious, for divination and healing. As it is potentially harmful, it should only be drank under the guidance of a shaman, who will both monitor your health, help you "see" more, and chant in the dark for hours on end. On the first use, yagé is likely to induce pretty serious vomiting and diarrhoea. If you are very interested in the drink, culture, and tradition it may be worthwhile to schedule two nights in a row with a shaman, which will really boost your chances of experiencing something more interesting.
You might assume that the remote jungle lands of Colombia might be the refuge of the FARC, but the fact is that much of it is too remote for even guerillas to operate. The extreme south is very safe (aside from natural dangers like snakes and insects!), and visitors should not worry about violence on a trip to Leticia. The area around Leticia, in particular, would be an impossible target for militants even if they were interested in traveling so far south—the Colombian military presence in its tri-border region with Peru and Brazil is immense. Western Putumayo and Caquetá, however (the extreme northwest of the region), are real hotbeds of guerrilla activity and should be left off all itineraries.
The Columbian Amazon is pretty remote. While bordering Pacifica and Orinoquía to the north, travelers are far more likely to be visiting the southern tip, which is cut off from the rest of the country, and more connected with adjacent towns and regions of Peru and Brazil.