Received the bed in a very tall but thin box. Perfect for hiding until Christmas.  After my grandson was asleep, it took maybe 30 mins total for me and my husband to put the entire car together.  We put up a mural of the grand prix behind it and my 5 year old grandson was beyond happy. The mattress does sit down inside and on the floor. With a small bunk bed box spring and a regular twin mattress, "perfect".