Let's take a field trip, you and I. To a place where we probably shouldn't go.
So, there's a small hidden area right on top of Diamond City, and I'm here to show you how to get to it. Behold:
To get to it, you need to climb a few buildings right outside the town. I used a jetpack to traverse these spots, but it's entirely possible to do it on-foot, too. It might just take a few tries and quick saves. And remember: if you do use your Power Armour, using your jetpack consumes more Fusion Cores than normal.
Eventually, you'll be at an area directly connected to the stadium. To me, it looks like a cafeteria of sorts. Within, you'll find a bed, a few random pieces of junk to loot, some slacks, and a mini-nuke (score!). That, combined with Power Armour station you can find there would suggest Bethesda intended for you to find this place, right? Even though it's a little out of the way and kind of random?
Well, maybe. Thing is, if you look out from the cafeteria area, you'll note a ton of glitchy things that happen depending on where you're standing. You can even kind of jump through a few walls up there. If you happen to throw yourself into the abyss, the game simply loads you into Diamond City proper. It's weird, but cool. Maybe it was supposed to be a bigger thing but Bethesda scrapped it? Who knows.
I want to also take this opportunity to once again suggest that you should totally explore Fallout 4 by using your jetpack. It's a kind of late-game unlock, given that upgrading your Power Armour for it requires you to have the Science! and Armorer perks at level 4, but it's worth it. Jetting around Fallout 4, going on top of buildings, and exploring with the jet pack is a blast. Sometimes, you might even find some neat stuff along the way! At the end of the video, you can see me flying around the rooftops of Diamond City, just for kicks. I can't wait to see what else I find out in the wasteland with my jetpack. Gotta use those Fusion Cores I've been saving up for somethin'.