I think this would be a neat idea for dungeons & raids. Yes I know that technically, at least dungeons, you can go exploring after clearing out the dungeon (raids not so much). Generally speaking once done they are considered "cleared", unless they get a 'Hard' mode in which case they are not, but once 'Hard' mode is done they are considered cleared again.

So would be a nice feature that if you had the ability to toggle "exploration mode" in options, where no monsters would be - but also no chest's, no loot, no xp, etc. Let you do it solo or find a group of others. With the only requirement is that you have "cleared" the dungeon/raid before hand (and Hard mode if applicable).