I live in a condo and my cat always stands in front of the front door and meows. I don't get why, because we've never let him out there. Even when we're about to leave the condo, he doesn't run out, he stands at the door until we leave. We have a balcony door and he never stands at it and meows. You would think that he would rather go out on the balcony than the front door because there's nothing beyond the front door. My guess is he hears my neighbours and wants to explore what's out there?
We let him go once to see what he would do, but he just sniffed around and then came back. He can meow for HOURS. I don't get why. I tried playing with him by pulling out his toy in another room and and he literally runs to play, but then he goes back and meows at the door afterwards. When I come to him while he's meowing, he just runs away then goes back. It's weird.