We arrived late at the evening but fortunately Christel has a straightforward check-in procedure with a security box which gives you the keys with a code.
The apartment is in a very nice neighborhood, in the historic part of the city. It is not very easy to find but Christel handed us a way-description via mail, which worked fine.
The apartment is clean and comfortable, but not very big, as you might imagine in the historic part of Lisbon. The apartment has an adjustable air conditioning, which is really nice. Overall: There is probably everything you need.
I really recommend staying in this charming apartment!