Using Hallucinatory Domains

The basic uses of the Hallucinatory Domain spell are punishment, prison, preserve, pleasure resort, or palace, or some mixture of these.

Punishment: The goal is a vengeance that the world will never forget. Greek mythology and Dante's Inferno have good examples of this. Such domains are generally pretty small: just big enough to include the elements needed for the torture. Since the domain is physically located in the real world, there's often no need to define the gross physical details, just the details of the punishment itself. For example, the mountain that Prometheus is bound to (or the cave that Loki is bound in) is not part of the hallucination; only the bounds themselves, and the tormenting vulture (or serpent, for Loki,) and the repeated action is defined by the spell. Similarly, the pool Tantalus stands in, and maybe even the tree nearby, does not need to be defined by the spell, only the behavior of the pool and tree (and the fact that Tantalus cannot leave the pool.)

Prison: The goal is control, particularly when the prisoner can't be harmed directly or may be needed later, as a bargaining chip or a source of information. The spell itself, not the rules it defines, prevents the prisoner's escape, so the rules usually define defenses to prevent attempts to rescue. Both Sleeping Beauty and Brunhilde are being punished, but also imprisoned; the wall of thorns or circle of fire obviously aren't there to harm the prisoner, but to prevent rescue. If the prisoner is more of a hostage than a criminal, the prison may also include elements of pleasure.

Preserve: As in "game preserve", although this can also include museums or barracks for employees. Consider Valhalla, where warriors in the service of Odin kill each other all day, then are resurrected so that they can feast and drink all night' Valhalla is designed to keep the warriors happy and well-trained for the eventual final battle. Another example would be the "devices" in The Piano Tuner of Earthquakes. A village-sized magical preserve would be something like Brigadoon. For that matter, the Talosians in Star Trek use their illusions to keep their prisoners content and (hopefully) allow them to breed and repopulate the planet. As for pocket universes, hallucinatory domains can be created to protect an object instead of a person, but then there needs to be a caretaker present to preserve the domain itself.

Pleasure Resort: Another domain that requires a caretaker, although usually a willing one. Pleasure resorts are designed to entertain, so outsiders may actually be welcome, as long as they follow the rules and don't threaten the resort. The best examples of this are science fiction rather than fantasy: Westworld, or the pleasure planet of Star Trek. However, there are also urban fantasy or weird tales about shops that sell magical gifts or exactly what you need, like "Shottle Bop" or "Bazaar of the Bizarre" or Needful Things. These shops often can only be found under special circumstances, or move around, or the caretaker may have unusual powers which may belong to the caretaker or perhaps are bestowed by the shop itself.

Palace: Wizards retreating from the world can cast the spell on themselves or on a steward to create a magical tower. The primary example is actually another (A)D&D spell, Guards and Wards (which just happens to be a 6th level spell...) It enumerates specific magical changes to a wizard's tower, but these could be covered by the rules of a hallucinatory domain much better. The strongholds of wizards in other media seem to have magical powers as well: trees and shrubbery that animates to repel intruders, walls that rearrange themselves, intelligent doors. Perhaps the strongest example, though, are haunted houses, even though the "target" of such a spell seems to be a ghost rather than a living person. But then, haunted houses seem to lie dormant until someone enters them, so you could decide that a "haunting presence" casts Hallucinatory Domain on a victim who enters the house (the wife in Burnt Offerings, the little girl in Poltergeist... the boy or the dad or perhaps both in The Shining.)

There's also a lot of potential in the idea of a lineage of caretakers. Some magical places -- Hogwarts, for example -- seem to outlive any particular magician or caretaker. This may be explained if the rules set by the spell-caster include a rule for how the role of caretaker can pass from one person to another. In the case of Hogwarts, the school's caretaker is probably the headmaster, although there seems to be some leeway in how long it can go without one. In one of the Dilvish the Damned stories, there are twin wizards who use a magical city as a game board to decide which of them will have magical power for the next decade or century; perhaps this city is created each time it is needed, but it's also possible that one of the twins is trapped in the location as caretaker and can only be released when the city is created and a hero finds his way through its maze.