I've done a bit of sandbox exploring on this map. In my searches, I've found quite a few references and easter eggs and I wanted to share them here.

Near the flooded generator room, there are folded cardboard boxes with Aperture Science logos on them.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070744

There is a train above the zs_blackout area of the map that reads, "Narre Packing; We ship goods for the dankest of price."
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070410

The closet in a storage room to the right of the bunker's entrance has a plush dino in it.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070463
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070437

A closet in the mall section has hidden money!
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070504
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070485

Going through this particular time warp has a chance to trigger a unique event.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526104950

At the very bottom of the main time warp, there is a breakable portion of wall with 800 hitpoints. Breaking the wall gives access to a room that contains dolls and a toaster, with writing on the wall that reads, "♥♥♥♥♥♥♥♥♥, It's the sacred toaster shrine."
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070545
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070565

There is a room right next to the pool that has a radio and an illustration of what I can only assume is someone's fictional character. Using the radio plays music, which I also infer is related to the illustration.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070704

Right outside that room is writing in blood that says, "Sideways, sometimes." This is a reference to the band Nine Inch Nails and their song The New Flesh, which the aforementioned statement is lyrics to.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070667

Towards the back of the mall section is another set of scrawls on the wall, this time saying "All the patterns fade." I think this might be a reference to the band Tweaker and their song Linoleum, which the phrase is lyrics to.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070526

Also inside near the balcony overlooking the forest there is blood on the wall reading "And all of this will never be the same again." This is yet another song lyric reference, this time for the Dave Grohl song Mantra. It also appears in the mall area, in the first room on the left from the entrance.

Two symbols found in the map are direct references to Nine Inch Nails' album The Slip, which contained art for select individual tracks on the album. The two that can be found on the map correlate to the songs:

999,999
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070587


and Echoplex, which Echofour Endtech is inspired by.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070638


And finally, there's this strange cassette I've found in the cafeteria. I'm not sure at all what it does, but it's worth noting that it only becomes a physics prop when interacted with, meaning something might trigger when it is picked up. I suspect it does something when rubbed on the right place, or it could be more useful in the actual ZS gamemode.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2526070620

That's all for now; if anyone finds out what that curious little cassette does, I'd be glad to know!