Los Nevados National Park (or Parque Nacional Los Nevados in Spanish), provides some of Colombia's finest trekking scenery. The National Park is extremely high, with various snow covered peaks. It can get very cold, and you'll need to allow time to acclimatize if you plan on spending the night.
Manizales is the nearest town to Los Nevados National Park, and from here you can arrange a full days tour into the Park. Generally, you depart in 4WD early in the morning and return late in the afternoon - you'll go right up to the refuge and snow line, have a bit of time for some trekking, and return to Manizles via some nearby hot springs (a spa hotel - either Termales del Ruiz or Termales de Otono). Various tour operators in Manizales offer such day tours. Trekking enthusiasts might consider arranging an overnight package - packages of up to 4 nights trekking and camping can be arranged in Manizales.
There is just one hotel inside of the park itself, called El Cisne. Another hotel just outside of the Park itself, but still in a lovely setting is Refugio Arenales. In addition, there are also the spa hotels attached to the hot springs mentioned previously.
See the section on trekking in Colombia for other ideas, or see the video of Los Nevados.
