A good budget option if you just need a cheap bed for the night for a stopover at Madrid airport, and you're comfortable sleeping in an apartment with a few young guys. It's within walking distance (15 minutes) to terminal 3, and from there a free shuttle bus can take you to the other terminals. Note the late check in time (9pm) and early checkout time. Also, you don't get a key to the apartment, so if you need dinner or a snack, it's probably better to take care of this before you check in, otherwise you have to make sure someone will be there to buzz you back in if you go out.