Harry modified his wooden doors upstairs by taking out the bottom panel and replacing it with Plexiglas, both the door at the top of the stairs and also the bedroom door of Sylvester's room. He did this so that when he'd come upstairs, he could see where the cats were. If they were by that door, then he'd go in through the kitchen door instead. For Sylvester's room, it allowed Sweet Thing and Sylvester to see each other without actual contact. They were always arch enemies though and never became friends. They were both in tact male cats and very territorial! It was very helpful though to see where Sylvester was before entering his room. Sylvester had feline aids so was kept separate from all of dad's other cats. He loved to be pet though and was usually "Mr. Nice Nice." Of all the cats I had contact with, he was the only real "lap cat."
The modified doors worked very well but had to be changed back when it came time to sell the house. Most people, after all, would want privacy in their bedroom so a door with a window in it wouldn't be a good thing.
When I asked my dad if he could make a door for us that we could use to close off the basement so the cats wouldn't go down there when we didn't want them down there, he designed this special door for us. He used Plexiglas in it so that the light could still shine through and also so we can see if someone or something is on the other side of the door. It works well and I'm very happy with it. So is my cat, Spunky Doodle. The other day she followed me down there but didn't come up when I did. My husband didn't know she was down there and closed the door! When I was going to bed at 10:00, I saw her on the other side looking in patiently waiting for someone to open the door for her. Poor Spunky Doodle! (She wrote about this episode on her cat blog on http://karen.pnn.com (Cat Corner-MEOW) section.