Practical tips
Best time
Practically on the equator, so there are no seasons in the European sense: altitude decides the climate. Bogotá is cool all year, Medellín mild, and the Caribbean coast hot and humid throughout. What changes is the rains, and they change from region to region.
Languages
Colombian Spanish is known for its clarity, especially in Bogotá, and is a good language to learn in. There are more than sixty indigenous languages, plus San Andrés Creole and Palenquero, the latter spoken in San Basilio de Palenque. English is current in San Andrés and Providencia.
Etiquette
Greet everyone on entering a room, use "usted" until told otherwise, and accept coffee when it is offered, which is nearly always. Talking about the armed conflict is possible but takes tact: it is recent and personal history for many people. The rest of the practical guide is in preparation.
What to see & culture
Places
The walled city of Cartagena, a World Heritage site; the Lost City in the Sierra Nevada, several days on foot; Tayrona Park between jungle and Caribbean; the Cocora valley and its giant wax palms; San Agustín and its pre-Columbian statuary; and the Salt Cathedral of Zipaquirá, carved inside a mine.
Culture
A country with both a Caribbean and a Pacific coast, three mountain ranges and Amazon, and a culture that changes with each. Cumbia and vallenato come from the north, currulao from the Afro-descendant Pacific, and García Márquez's magical realism describes a place that exists. The 2016 peace agreement opened regions that were closed for decades.
Food
Coffee, obviously, but drunk short and sweet rather than as exported. The bandeja paisa is a whole meal on one plate, Bogotá's ajiaco is a three-potato soup with corn and guascas, and the arepa changes shape and filling in every region. Fruit is the real luxury: dozens of species that never leave the country.