Keep in mind you have Very powerful spells at that level. You could cast Antipathy (Orcs) on your robe.
I missed this the first time around. Much thanks to @
schnee for highlighting it. And thanks for posting it.
This is EXACTLY the solution I'm looking for. It's a time-constrained solution to the PCs problem that doesn't absolve them from participating in the rescue, either by putting them on the sidelines or making them superfluous. Perhaps more importantly, it's not a peak ability.
I can accomplish this with a 15th-lvl wiz! That's phenomenal. My world is pretty low-power, so high-level characters are few and far between.
The orcs have some non-orc creatures accompanying them and other non-orcs under their control, but they're not going to be sophisticated (or stationary) enough to rely on Hallow, Forbiddance, or other spell defenses. On the other hand, not all the hostages will be in the same place, so the PCs will need to be somewhat daring to rescue all of them. An Antipathy robe will be incredibly helpful.
And, for general illumination, we are dealing with an open-air situation. Not as bad as a sports stadium, but the analogy is apropos. Lots of orc campsites surrounding a central camp with more powerful action and resources, and of course, the hostages. My "Tears of Grummsh" (groups/tribes of roughly 50-100 orcs) trickle off the main Eye to scout and forage, returning to the main mass with food, slaves and information.