If you center on the Watch app on your Apple Watch apps page, you can use the digital crown to slowly zoom into it. It’s a wonderful detail, as your watch face will build as you zoom. It reminds me of holding the Shift key on Mac when clicking Minimize in a window. You can see a longer demo on the Finer Things in Tech YouTube channel.
As far as I can tell, no other apps do this, including Apple’s own. I don’t know whether Apple provides this mechanism to third parties, but it would be fun to see this more often.
Via Benjamin Mayo, this is apparently even cooler with the Solar face. Sounds like Apple did this for a bunch, or maybe all the faces.