Not the most obvious place from outside (we walked past it), but worth finding out for lunch or a light meal when in Madrid.
For the very reasonable price of €11 you get three courses, bread and a drink. The host was very welcoming and had reasonable English. There was a limited choice (the menu changed daily) and nothing to indicate what was vegan when we visited, but it was happily pointed out what was suitable or could be made suitable when I asked. I had a simple Miso tofu soup followed by a delicious filo pastry filled with curried vegetables (rather like a big samsosa). My partner who is veggie had a fresh green salad with tomatoes then spaghetti with sun-dried tomatoes and veggie parmesan. Choice of drink included soft drinks, beer or wine.
Sadly the desserts weren't vegan on our visit and I had to make do with some fresh fruit. This would have been good if it had been a mix but I was given the choice of one from two or three different fruits and ended up with some banana chopped up in a bowl...
Overall a relaxed and enjoyable meal in a non touristy taverna and very good value.
Cons: Limited choice, No vegan dessert