In video games with wide open worlds built onrevisiting the same locations over and over, there are certain places that you can only enter once and never again. Sometimes this is because the place no longer exists thanks to being aDoomed Hometown or aCollapsing Lair. Sometimes it's because the plot keeps you out of it. Whatever the reason, these are places that can never be returned to.
The items inside the dungeon are frequentlyLost Forever and there are often times that you can only fill up yourMonster Compendium by grinding there.
Note: In order to qualify a game must be generally be open toBack Tracking and not just have a linear advancement through it.