We got all of his stuff ready and packed, and packed him up and took him over. He meowed (not his half-mew, but full meows, with lots of the "oh" emphasized) the entire way as he usually did on car trips. We brought him in, and kept him in his carrier at first while we carried in all his things. As soon as we were finished and had his litterbox and food/water dishes set up, and toys set out (including his kitty condo that we'd gotten while he was still at my grandparents'), we let him out to explore.
He started roaming around right away, looking everywhere and sniffing everything. He wasn't scared at all, perhaps because I was there or perhaps because he'd "been there, done that, got the t-shirt" with the whole moving experience. He settled right in, immediately locating his food, water, and litterbox, not to mention his toys, condo, and favorite blanket (which I'd put on the foot of my bed). It turns out I had plenty of time home from work, including the weekend, to get him acclimated to the apartment, even with me being gone a good portion of Thanksgiving Day. I also have a sliding glass door, although I have vertical blinds instead of a nice smooth curtain to walk behind, and the view isn't anywhere near as good as it's just a little porch with a fence most of the way around it, blocking most of the outdoors. He quickly discovered he could peek his head through any part of the blinds, and that he also liked walking behind them.
After a while I decided to leash-train Squeeker, and that was definitely interesting. I put the harness on him (you never put a cat's leash on a regular collar) and he hunkered down and rolled, I guess trying to show how "heavy" and uncomfortable it was, and to get me to take it off. It took a few minutes to get it on him too, because the buckle was at his belly instead of at the top of his back (manufacturers take note!), making me hold him on his back. He eventually got upright, but hunkered down the way a cat hunkers when stalking, only he was definitely not stalking anything. I attached the leash, and started towards the front door. He wouldn't budge, so I picked him up and carried him to it, putting him down right in front of it. I opened it, and it took him a minute to realize that I was leaving it open and not stopping him. He belly crawled just outside, still disliking the harness. I quickly shut and locked the door so we could continue our exploration.
Squeeker seemed happy checking out the space underneath the stairs to the second floor, which made things difficult with the leash, so I coaxed him toward the outside door. I held it open for him, and he stood in the doorway sniffing the air for quite a while. We finally ventured outside, very cautiously of course. After all, it's a big world out there that he's never really seen. He was shivering too, though it wasn't cold outside, so I think he was a little worried in spite of being curious. I figured I'd let him take the lead, and we'd go wherever he wanted (except other people's back porches and up trees of course) and go back in when he wanted. Our first outdoor visit lasted about 20 minutes, and he mostly just explored the bushes in the immediate area before pointing us back to the apartment door. And, of course, it was just as difficult to get him to stay on his back for me to unbuckle his harness as it was for me to buckle it, despite the fact he didn't like the harness.
Eventually, after a few walks on his leash and harness, he got used to the harness, no longer hunkering down in it. It got a little easier for me to buckle it on him too, because he didn't put up quite as much fuss after a while. He even figured out that it was okay to roll on his back after we came back in, because that meant he'd shortly be harness-free and he still thought that was a Good Thing. Our trips became longer, often lasting over an hour, especially since he loved being out and due to weather and other things, he didn't get to go out very often. I'd follow where he led, only restraining him from exploring others' porches and going too deep into bushes. Oh yeah, and I didn't let him go between the bars in the fence surrounding the pool either, not only because I couldn't follow but because we just plain weren't supposed to be in there (it was still "off season" for people, and cats never belong in there). I sometimes guided him to walk towards the apartment office and we'd go inside and say hello to the managers there that day. One in particular loves cats, and totally fell in love with Squeeker from the moment she met him. She told me that any time I was going to be out of town and needed someone to peek in on him, to call her and she'd love to do it.