So, in Dungeon of the Mad Mage, there are various gates that Halaster set up to travel from floor to floor. If you can figure out how to activate one, you can use them too, but if it would take you to a level you're unprepared for, then the spirit of his former apprentice will block you from using it, though you can still look through. A wish spell is the only way to force your way through. (The book does say that, as a DM, you are allowed to waive this rule and let them pass at any time, particularly if you truly think your party can handle what's on the other side.)
So the party finds a mirror at the end of one of the hallways on the first floor. The mirror's frame has a single image engraved into it, that of a wizard holding a wand. The rule for the gate is simple: touch the mirror with any wand with at least one charge remaining, and it opens for one minute to an identical gate all the way down on level 10.
Now, in the previous session, the party happened to find a wand of secrets, so they already had everything they needed. One used detect magic, and I told them the mirror had an aura of conjuration magic to clue that it was a magic portal. They even remembered they had the wand, so I was sure that "touch the mirror with the wand" would come up as one of the things they'd try. Maybe not first or second, but surely they'd figure it out, right?
Here's a list of everything they tried that I can remember the first time they reached the mirror:
- Touch the mirror.
- Bang on the mirror.
- Hit the mirror with a warhammer. (Even crit and everything, hammer just bounced off.)
- Cast dispel magic. (Halaster's gates are immune.)
- Expend a charge of the wand at the mirror. (The wand only shows secret doors or traps, and the gate is neither. Also it didn't open.)
I will mention that one of the first things I heard one of my players say was "maybe try touching the mirror with the wand," but this suggestion apparently got lost in the shuffle, and he never brought it up again. That made it all the more maddening.
Eventually they gave up and continued elsewhere. Nearby, they found an alcove where, if you wore a bronze mask of Halaster that they previously discovered and entered it, you were teleported to a demiplane where a Halaster simulacrum would answer any three questions about the dungeon, lying on the first answer and telling the truth on the second and third. The party member who went through, having no idea what to ask, decided to burn two questions asking the simulacrum how to open the mirror (the third was about a couple of blocked passages they'd encountered earlier, which I told him had absolutely nothing behind). Well, at least it gave me an easy way to just tell the answer so they didn't get stuck, and the lie was obviously a lie ("speak friend and enter"), though I made sure to have the simulacrum ridicule him about how simple the puzzle was both times (hey, it's in character for Halaster).
So, he tells the party, they go back, touch the gate with the wand, and it opens. They try to go through, but they're blocked. They try basic methods of getting through first, like running at it and beating on it. They can see archery targets on the other side, so one member tries shooting a bolt through. Having no rule on whether objects can enter a gate that players can't, I decide to allow it. A couple of attempts and he hits a target, but he still can't enter. They then get the idea that they have to hit a bullseye to allow them to go through, so he tries again and again until the gate shuts. They reopen it and keep trying, with everyone just constantly firing bolts through the gate.
After about the third round of this, in the interest of moving the game forward, I decided to just have the voice of Halaster's apprentice spell it out for them and tell them telepathically, "How much more obvious do I have to make this? You're not ready to go through here! Turn back!" She's only supposed to message players if they attempt to go down the stairs to the next level early, with the magic block on the gates in theory acting as a sufficient deterrent to leave. Not for my party, apparently. They had a good laugh about it as they left and were intrigued by the fact it was a female voice.
I could have just let them through, but I had nothing prepared for level 10 (hell, I haven't even started prepping level 2), and it would assuredly have been a TPK. Maybe a good lesson on not taking strange portals, but there
are gates I'd actually like them to traverse in the future, and I'd rather not embed the idea that all gates are instadeath in their minds so quickly.