This is a tricky one. It's kind of a guide+exploit at the same time, because you end up using a server bug. Tested on C4 servers.

Here is an easy way to bring up your low- level character, especially if it's a mage, in necropoli and catacombs.
Let's pretend you have a lvl 20 warrior (insert your level and proffession), and want to level him to 27 in a day.
We all know that catacombs are a lot of fun with a party, or even solo. But on low levels it is a lot of work to level solo there, plus the agro mobs that chase you all around the place unless you kill them (losing precious hp and risking to bring upon yourself all the mobs that are not agro, but social towards the agro ones, and most likely die).
So what you do is this:
-Go to catacombs that are about your level, get in, and in the very first room make every single agro mob attack you. Then, once you've got those guys on your tail, run to the gateceeper, and port out of the catacombs, but first make sure that the agro mobs follow you all the way to the gatekeeper. Now, youre out of their reach, and they will try to go back to their base positions. But due to some magic reason, they can not leave the gatekeeper room, and lose their agro status(!).
So unless you attack them, or anybody kills them they will either:
1. Stay there. Period.
or, most likely one,
2. Walk back to their initial positions, but that will take a load of time, so you've got about 30- 40 minutes of worry- free leveling, after which you just repeat the process.

Now youre free of vexations in the shape and form of social agro mobs, and can easily level you character on those that are left. This works in every catacomb or necropolis in the game, and can be done with any level character in the appropriate places. Search the gradation of cat/necro's by level on google, youll get tons of results.

That's how i brought up my Titan ;)