In my campaign, the ancients were more advanced in their use of magic. This was supported by the Collegium of Mages. Each ancient city had its own college of magic that was a way for weeding out the bad apples and ensuring that the wisest and most skilled wizards powers were put to good use.

When civilization collapsed, those ancient halls became a dangerous place for all but the most intrepid or foolish of adventurers. That’s where all the good stuff is!

How does a current city in a high magic setting handle the organization or lack there of of its wizards?

For a fallen city, what kinds of things might there be found in the haunts of wizards?

In addition to magical devices, like weapons, armor, wands, ring, etc. there could be rooms, statues, golems, familiars, imps, homonculi, trapped creatures, magical traps, and many other kinds of things to make going their both interesting and dangerous.

What kinds of experiments might be found there?

Would lanterns or other devices with continual light or continual darkness be common in such a place?

Would there be special devices, phrases, or other means to safely access these areas?

In my campaign, there are different levels of amulets that enable the wearer to enter such areas, in addition to showing their rank.

Would a geas be placed on the unwary to get some item needed to restore the guards and wards making it harder to get in?

All magic users and illusionists had copper or bronze medallions that were non-magical and merely showed one as a member of the Collegium. As the medallion tarnished or aged, one knew their skill level was advanced. Much like the black belt derived from the accumulation of dirt and grime on the belt.

At the level of Wizard, 11th level, the wizard received a silver amulet, gold for Mages at 16th level, and platinum for Archmages at 18th level.