El tigre is a very popular bar among students in Madrid. If you are hungry after the whole day walking this is your spot. When you order your drink (a pint of beer or tinto de verano) you get a huge amount of tapas, usually bread with cheese, patatas bravas, tortilla de patatas, Spanish ham or chorizo...
It's usually crowded after 21h of Spanish or exchange students since you can get easily full by ordering one drink if the group is 4 people. Food is not the best quality but helps when you are starving and don't want to spend a lot.
They have two "El tigre" in the same street so if one is full check the other one.