A good Hostel is the Amigo hostel, they do some realy good day trips to the Mexico city pyramids ( take a hat and lots of water) also they do a free walk around the city (I didn't do but wished I so had) If you want to learn how to cook Mexican food, They also do a day trip to the markets and then show you how to cook the food ( best part is eatting it) I was only in the city for a few days but there is always a toure or day trip going on. don't do the flower garden trip. The Zoo is really big and you could spend a day there and not see everything, Really recomend that, best of all it's free. be careful of where you eat as all the people in my dorme ate street food and came down with the stomache bug, so just be weary of the street stalles.