Like, I once bumped into a fully stocked and operational Coke machine in an unlit maintenance corridor twenty feet below ground level. Its display lighting was the only illumination for a hundred yards in either direction. I don't even know what it was plugged into.

Somewhere below this city there's a room the size of a high school gymnasium filled floor to ceiling with rotting mattresses. I've seen it with my own eyes – and, more importantly, smelled it with my own nose. I can't recommend the experience.

(That last one isn't even mysterious. The room in question is within easy walking distance of the basement of a major hotel, if you know where you're going; I imagine the hotel started stashing their old mattresses there at some point rather than pay to have them hauled away, and over the ensuing decades the situation got out of hand.)

In response to a couple of recurring questions in the notes:

1. I don't have any experience with the weirder corners of university campuses – my work in that particular job just never happened to take me there. I did, however, once have to do a cable trace in the basement of a former Christian elementary school. It had haphazardly been subdivided into numerous tiny rooms, some as little as ten feet across, with no central hallways or apparent floor plan. Every single room was, for reasons that were and remain unclear to me, full of broken kitchen appliances. One room in particular contained an enormous industrial freezer unit that was larger in its smallest dimension than any of the doors leading to it. Was it delivered in pieces and assembled on site? Did they build the room around it? That one still bothers me a little bit.
   
2. No, I did not drink the Morlock Tunnel Coke. What are you, nuts?

“spicy pillow” jokes aside, I think @flowerkrone​’s tags deserve a serious reply:

#my old phone looks like this on my shelf lmao #im too scared to touch it to throw it away #idk what trash this even goes into when its at this point

The pillow-shaped object here used to be the phone’s battery. It’s not a battery anymore. Now it’s a balloon full of corrosive, pyrophoric chemicals and hydrogen gas and it’s one puncture away from burning your house down. I am 100% serious. You should be scared to touch it.

But you gotta touch it, because you gotta get it out of your house before the pressure builds up to the point where the balloon pops. This isn’t going to happen soon – there is no need to panic – but it will happen eventually.

And, indeed, it doesn’t go in the ordinary trash. You put this in the ordinary trash and you’re gonna set the garbage truck on fire. Don’t do that to the garbage collectors, their job is hard enough already.

The first thing you need to do is get a fireproof container. The most common household item that qualifies as a fireproof container is a cast-iron cookpot with a cast-iron lid – often sold as a “Dutch oven.” Any other cooking container that’s unreactive, has a very high melting point, and has a lid made of the same materials will also work: enameled or stainless steel, Pyrex with glass lid, etc.

However: Do not use a pot with a PTFE-based non-stick coating. If the battery does explode, the fire will probably be hot enough to degrade a PTFE coating, producing toxic smoke. (Not that you should breathe the smoke from the battery fire either, but PTFE breakdown products are worse.) Do not use a pot made of aluminium or copper. The fire might even get hot enough to melt those.

Whatever container you use, you might have to throw away along with the phone, so don’t use your good Dutch oven for this. Go to a thrift store and buy a cheap one.

Once you have the fireproof container:

1. Gently pick up the phone and put it in the fireproof container. If possible, gently tape the phone to the bottom of the container to prevent it from bouncing around. Don’t put any padding in there, that’ll just make a fire worse if it does happen. Put the lid on and tape it shut.
2. Put a label on the container, something like “DEFECTIVE LI-ION BATTERY – FIRE HAZARD”.
3. It is now reasonably safe to move the container around. However, if the battery does explode, the container is very likely to leak smoke and get hot, so keep it in a well-ventilated area and away from things that will be damaged by heat. Don’t leave it exposed to the weather, either.
   
4. You need to find either a hazardous waste disposal site, or an e-waste recycler that will accept defective Li-ion batteries. I can’t help with that because I have no idea where you live.
5. However, your local fire department, if you have one, will probably be happy to help. Call their non-emergency number. Nothing is on fire yet, so this isn’t an emergency, but things that can easily start a fire are still within the fire department’s responsibilities. Tell them you have a phone with a bulging lithium-ion battery, you put it in a fireproof container, and you want to know how to dispose of it safely.
6. If the fire department tries to tell you this isn’t dangerous or it’s okay to throw it out in the regular trash (with or without fireproof container), hang up on them and write a cranky letter to your local government representatives, then keep looking for a proper disposal site.
   
7. When you do find a a hazardous waste disposal site or an e-waste recycler, call them and make sure they will take defective Li-ion batteries, before showing up. That’s also a good time to ask if they will let you have the fireproof container back.
   

PSA.