Pulqueria Las Duelistas in Mexico City, DF
Let's talk about pulque. Pulque is a traditional Mexican drink made by fermenting the sap of certain agave plants, namely the maguey plant. It's alcoholic (but low in alcohol) and used to be drunk during rituals, but now you can pulquerias around Mexico. A great example that you should visit is Pulqueria Las Duelistas in Mexico City near Mercado San Juan. This place has been around for more than 80 years. Oh, and they're open from 10 am and yes, they only serve pulque (and snacks to go with it), because day drinking is awesome.
No one knows when pulque was invented - it's been around for thousands of years. Pulque is viscous and a bit sour. It may be a bit of an acquired taste, but I really liked it!
Sugar and natural flavorings are typically added to the sap to slow down its fermentation, since if it's fermented too much, it's no longer drinkable. At Las Duelistas, you can get it in fruit flavors like guava, coconut, pineapple, etc.