The hotel web site mentions public outdoor parking - a euphemism for "we don't have a car park but you can park nearby". It also mentions that you need a flight ticket and passport to get in. What it doesn't mention (but what I believe to be the case) is that you can't take your luggage with you, other than a carry-on bag, as the hotel is airside.

Coming from Germany (=Schengen) the OP would have to go through outbound passport control to check into the hotel, queue up for passport control again to leave the hotel to go into town, and go through the whole rigmarole again each time he wants to return to his room for any reason. If he has checked baggage he would have to go landside to pick it up and then either try to check it straight in for his onward flight (if they let him), or put it in a baggage locker (and leave it there until the next morning because each time he accesses it he would have to pay again).

The Mercure is great if you're in transit - but not really a practical proposition if you want to leave the airport.

This is what tripadvisor.com has to say about the hotel.