According to the manual, there should be a tomb on the east side of town.

"If you want to advance the storyline, choose the west mine entrance (on the left side of Torchlight), but if you want to quickly build levels, check out the tomb on the east side of Torchlight"

But where is it?

At the right I can find what looks like a cemetery when crossing a bridge to the bottom right. But I cannot find any entrances or levers or anything here. Is this not the correct place, or am I missing something very basic?
Like is it only available when you reach a certain level, or finish certain quests - or do I have to look somewhere else?

I believe it only opens up once you've completed the main quest.

Then there are two characters that have quest to complete. And I do believe you have to complete the main quest by winning in the bottom level.

Note that as soon as you finish the main dungeon with one character, the Shadow Vault will be opened for ALL of your characters. It's usually a bad idea to head there at level 1, though...

Thank you for your replies.
The manual made it sound like something that was available from the very beginning, as a place to fight and level up.
But the quests from Hatch keeps me plenty occupied when I just want to fight, earn gold and look for stuff, not advancing the main story.

I believe you can also purchase Maps from the Gem Trader to access mini-dungeons with a Boss in them?