"Invest in Colombian real estate" isn't one market — it's at least three, and they don't behave the same way or attract the same buyer.
Medellín
The default answer for a reason: strong foreign demand, a well-established digital nomad and retiree population, and a rental market with two distinct segments — short-term furnished rentals catering to remote workers, and long-term unfurnished rentals for locals. El Poblado and Laureles carry a foreign-demand premium; that premium buys convenience and walkability, not necessarily better fundamentals than nearby Envigado or Belén, which see less foreign buying pressure for comparable square footage.
Medellín's climate (year-round spring temperatures, thanks to elevation) is a genuine differentiator that shows up in long-term rental demand, not just marketing copy.
Bogotá
Colombia's actual economic center — more corporate tenants, more institutional-grade buildings, and a rental market driven more by local professionals and relocating executives than by foreign retirees or remote workers. Yields on paper can look thinner than Medellín's foreigner-facing short-term market, but the tenant base is more stable and less seasonal. Bogotá is the city to consider if the thesis is "Colombia's economy" rather than "Colombia's lifestyle appeal."
Altitude (2,600m) and traffic are the two things every Bogotá guide undersells until you've lived there.
Cartagena
A tourism and vacation-rental market, full stop. The walled city (Centro/Getsemaní) commands prices closer to a European resort town than the rest of Colombia, driven almost entirely by short-term vacation rental demand and a limited, historically-protected housing stock. Cartagena works if the plan is a vacation-rental-yield play in a supply-constrained tourist core — it works poorly as a "live here full time and rent long-term" plan, since the local long-term rental market is much smaller and less liquid.
Liquidity, ranked
Medellín and Bogotá both have deeper, more active resale markets than Cartagena, where the buyer pool for walled-city property is narrower and more foreign-tourism-dependent. If exit liquidity matters to your thesis, that's worth weighing against Cartagena's higher headline yields.
The short version
Medellín: lifestyle-driven, foreigner-facing, strongest short-term rental demand. Bogotá: economy-driven, more institutional, more stable long-term tenant base. Cartagena: tourism-driven, highest headline yields, thinnest resale liquidity. None of these is objectively "best" — they answer different questions.