Originally I did install cat flap door, one of those plastic things to door that separates two rooms, however one of my cat made it a cat hole by running like fire would been under his tail and ramming to door which split from impact, unrepairable really as I could not find enough strong glue for that.
They did like it better without flap door, so I never got around to replace it and I think it was much better looking without the flap.
They did like it better without flap door, so I never got around to replace it and I think it was much better looking without the flap.