You create a magical restraint to hold a creature that you can see within range. The target must succeed on a Wisdom saving throw or be bound by the spell, if it succeeds, it is immune to this spell if you cast it again. While affected by this spell, the creature doesn't need to breathe, eat, or drink, and it doesn't age. Divination Spells can't locate or perceive the target.
My question is, is there any reasonable way to get someone out of the various forms of the imprisonment spell?
It seems like, if they fail the save, it's basically just an instant, permanent imprisonment. The spellcaster can state conditions under which the imprisonment can be broken, but they aren't required to, and as a result, they could just leave the imprisoned one stuck in their tomb for life. Is there a way for someone (not the imprisoned one, obviously) to break the imprisonment if there are no conditions for its release?