This is a wonderful spot and well worth seeking out for lunch or an early dinner. It's actually one of the city's oldest vegetarian restaurants, founded sometime in the late 80's. Nice space with plenty of room, delicious Antioquian specialties like chicharron soup and even the occasional bandeja paisa. Creative healthy juices (like flax seed) and regional sweets. Also has a small but well-stocked shop.
It's in the neighborhood of Itagüi which is hardly ever visited by foreigners, but is very easy to reach. 10 minute walk from the metro, I highly recommend spending some time in the lovely park which has a real neighborhood feel (the restaurant is just two blocks away). Friendly service and pleasant atmosphere, a living piece of Medellin veg history. Note that of Feb 2012 the listing is updated w/the correct address and map location.
Cons: Out of the way, Closes at 6