Post Mercenary Leveling Guide - Acrylia Caverns
There are two main parts to Acrylia Caverns - you have the castle which is the highest level part of the zone and outside of the castle. On the map above outside the castle is marked with the blue box, 45 - 55. Inside the castle is marked with the large red box, 55 - 63.
If you couldn't already figure it out you'll want to stay outside the castle until at least 55. Then you can slowly work your way into the castle. As long as you avoid the throne room and the upper floors as well as the jail cells in the basement you should be fine inside the castle solo with a mercenary.
Acrylia Caverns Original Almar's EQ Leveling Guide
This guide may contain errors or inaccuracies since the game has changed a lot since I wrote it.
It also contains a lot of information not found on this page about the zone and the mobs in it.