Mine

If you follow the old road west from Slagtown, past the Chemical Plant, past the Abandoned Highway, and even past Lurleen, eventually bombs start getting thrown at you.

That would be your cue to book it north, and hope that you can climb. After a 10m climb up, you can enter the Old Mine.

If you can't climb, don't despair! Follow the road to the washed-out bridge, and jump down--follow the river west until you go down a waterfall, then head northwest to dry land. Just follow the path there to the 1st basement floor entrance, and hope you don't aggro any yetis.

Denizens

The mine itself is home to some of the following post-apollyonic critters:

First Level
bats
cave rats
chukkas
bandits
cave slugs

First Basement
chumans
chukkas
vampire bats
giant spider
chuman guards/digger guards
cave slugs

Second Basement
grues and other scary shit
chimaera
cave slugs

Goodies

There are two mutations located in the mine; low-xp players may want an escort or, failing that, to put everything in their safe deposit box, apartment, or corp HQ and just suicide-run it.

On the first basement floor there is a Blacksmith's Forge; sometimes vampire bats hang out there, so watch out! They seem pretty good at dodging.

There are also a reasonable amount of items just lying around. If you find a pickaxe, you can mine here. Most parts of the mine yield bertrandite, acanthite, greenocite, and the like, but if you know where to look you can find rarer fare, including (but not limited to) rubies and diamonds. Searching a few select areas may turn up lesser ores and gems.