By and large, the answer to this is yes! Most areas in Colombia have stabilised enormously in recent years, with the area around El Rio in particular improving vastly. Colombia has a chequered history and is still recovering, however tourists on the coast can now travel safely to areas that up until as recently as 15 years ago were no-go zones.
Having said that, like any country Colombia has areas that aren’t as safe as others. Avoid walking alone at night in big cities and be careful about which areas of the city you visit. Big cities like Medellin and Bogotá have no-go areas, whereas the more touristy areas such as Poblado in Medellin are largely very safe; the north of Bogotá such as the area around Parque 93 and the Zona T are pretty safe at night, whereas La Candelaria (where most of the hostels are located) suffers from more petty crime after dark.
Most bad experiences start with travellers not taking these basic precautions. Walking around quiet streets after a night of partying and entering into transactions with unsavoury characters can be sure-fire ways to end up in trouble. Basic common sense should me your most trusted source of advice. If something feels unsafe, then it may well be so take a step back and be smart!
In a nutshell, Colombia, as with any other destination, is as safe as each person makes it.
For further reading check out what the Lonely Planet has to say.
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