Aside from being incredibly difficult to find, the hotel within the airport (Terminal 1) is very…read moreconvenient. Unfortunately that's by far its best benefit.
Disregard the note on their site that check-in is not 24h - I contacted them to confirm there's always someone at the front desk. Unfortunately they didn't respond to my question about how to find them within the airport.
Assuming you're staying in between flights, you'll have to exit and then re-enter security. To find the hotel, go down to the main floor where families meet arrivals and then back through the cafe area to the back wall. To your right (after the Caixa bank) there should be a set of doors and walk way leading to a new building with the Business Center, which is where the hotel is.
Our room reeked of unidentifiable food from check-in through the morning, so much so that I was worried it would permeate my hair and clothes. We were also greeted by several flies in our room. There is no duvet, only a sheet. To suffice, we pulled out a nasty blanket from the closet and laid it on the lower half of the bed. The shower door doesn't close and its lining isn't sealed tight so water leaks out, covering the entire bathroom area. The hair dryer overheats and shuts off after ~30 seconds, which means it took 20 minutes (mostly waiting time) to dry my hair.
The room is actually not too tiny, even for 2 people. So if you've got a quick turn between flights, it may be worth sucking it up (and forking over the $$$). But if I had to do it again, I'd rearrange our itinerary and stay offsite.