I moved with the cats last Tuesday. I thought about keeping them confined to a single room for a few days. D pointed out that they had been cooped up for the movers all day Monday and in the car all day Tuesday, so it would be ok to let them roam the whole house. That turned out to be a bad decision. By Wednesday afternoon, I thought I had found all the really good hiding places and blocked access to the unsafe ones. Sometime Wednesday night, Eliza vanished. She managed to find a basement access point to the subfloor under the laundry room. It turned out to be one of those I can get in but not out access points. There is a cat sized opening above the pipe indicated in the photo.
Friday night, we looked into every corner and concluded that this was the one place she might be that we could not see into. When we heard little meeps and meows from that space after D called her name, we left some very stinky food on top of the pipe. It disappeared. After the movers left on Saturday, we did some minor demolition in the garage and found another access to the same space; this one does not require a blind leap down 3 feet. We left more food at that opening, and it disappeared while we were out having dinner. D decided to camp in the garage to try and coax her out of hiding (since she was still mad at me for forcing her to spend a day in a cage in the car). He had been asleep for less than 45 minutes when he woke up to "meep" and a snuggling cat. He immediately put her into kitty prison (in the master suite with her sister) and rewarded her for coming out of hiding with more stinky food.
This morning, we built the door between the finished and unfinished parts of the basement. In a week or so, we will paint it and do a better job mounting the hinges. As soon as we unpack enough to get rid of the box obstacle course, we will let the cats roam the whole house again. With no access to dangerous places.