Antisana is Ecuador's 4th highest volcano and one of the least climbed. It has a reputation for being a difficult and dangerous mountain that isn't completely unfounded. It's active glaciers make routefinding a significant problem and it is easy to find yourself lost in a city of seracs on the upper glacier. It doesn't help that the "Standard Route" described in the lasted editions of the climbing guides isn't the standard route any longer due to its length and crevasse difficulties. There are 4 major peaks along its crater rim, of which the highest is the easiest to climb and first was crowned by Ed Whymper and the Carrels in 1880. The crater itself is filled with glacial ice and appears to be extinct but is not. It last errupted in 1802. The surrounding area has numerous lava flows. Perhaps the most well known is one just outside of Papallacta. The road to the peak passes a large lava flow that is being mined for construction material. Part of the beauty of the mountain is its serenity and spectacular views of Cotopaxi, Sincholagua, and Cayambe. The lucky will see condors. Everyone will see wild horses running around the bone-filled paramo. It is a majestic setting.
From Quito it is about a 3 hour trip. Take a bus to Pintag (1hr). In Pintag hire a camioneta and driver to take you up to L. Santa Lucia (2hrs). Be warned that not all of them know the way. Don't forget to secure written permission from the landowners first! See Red Tape below.
Antisana is surrounded by private property. This is also the reason the formerly popular Condor Trek (Antisana to Cotopaxi) isn't really doable in it's previous incarnation. Too bad because it is extraordinary. Anyway to climb Antisana you need permission from the landowners to pass through their property. This permission is secured in Quito for $10 per climber. The number to call is 02/455697. Pick up the permit in person. Climbers need to show the permit at the first guard post and surrender it at the second. It is good for drop off and pick up.
The best months are the "dry" December through February. This mountain is known for being cloudy however.
Camp anywhere. No fee but no facilities. Pack in and pack out all trash of course. Unlike so many of the other high volcanoes, there is no climbers hut.
Good luck finding accurate information about conditions on the mountain. It isn't far from Quito but you really cannot use Quito's weather as an indicator. It is not a widely climbed mountain but you can try the SAE: For general route conditions the South American Explorers maybe have people that have climbed it recently among their members. They also try to keep a bulletin board updated with climbing conditions on the volcanoes in the Quito clubhouse. Generally you can get some free route information by asking at the various climbing agencies too.