Leticia is a small town on the southern-most point of Colombia on the border with Brazil and Peru. The area is known as the Tres Fronteras (3 borders). Originally claimed by Peru and also Ecuador, the border was eventually agreed south of the Putumayo river and the area given to Colombia. Despite this, there were wars between Peru and Colombia and eventually the League of Nations had to step in and settle the dispute in the 1930s. To reinforce sovereignty of the area, the Colombian government encouraged settlement from other parts of Colombia. In the 1970s and 1980s, the area became a major drug smuggling point.
These days, tourism is the number one industry in Leticia. The city itself is a shit-hole with heaps of rubbish all over the streets. There is no nice Malecon (promenade) along the river to watch the sunset and the central square is a dump. At 5pm every day hundreds of parakeets gather in the trees in the main square creating a huge racket.
From Leticia, you can walk across the border into Tabatinga in Brazil, a city of about 100000. It is an even bigger shithole than Leticia, so there is no need to go there.
The real attraction is the surrounding jungle. You make boat tours up the river, visit natural reserves, go hiking in the jungle or make night safaris. On the Colombian side, you can see one of the world’s tallest trees, the Ceiba, which is unfortunately quite rare these days due to deforestation. I did one trip up the Amazon visiting Monkey Island and other points of interest along the river, also crossing over to the Peru side. The trips are quite expensive – for example just to enter Monkey Island, walk along a wooden bridge and see monkeys for 10 mins costs 30000 Colombian Pesos (US $12 at the time of writing). That’s as much as the entrance for St Paul’s in London.
You can get to Leticia easily from Bogota with regular cheap flights with both Avianca and LAN. Alternatively, there are flights 3 times per week to and from Iquitos in Peru. You can also take the slow (3 days) or fast (12 hours) boat to Iquitos.