D&D 5E Core Spell Options to Trap a High Level Dungeon

All,

While of course as a DM I can create any kind of trap I want, I want to know what the quick spell options are to set up a high level dungeon "by the book". Again, I recognize that I can create a million custom trap options, that I am not restricted in any way. I am just trying to better understand the core options at my disposal.

So far I see the following main options that have an indefinite duration useful for traps.

1) Glyph of Warding: Seems to be the go to trap spell, which can then kick off all manner of other spell effects.
2) Guards and Wards: Not really much in the way of traps but at least offers some deterrents.
3) Hallow: Can add some nasty effects to a room.
4) Symbol: The high level Glyph.

Any other good ones, including Xanathar's I should look at?

Those are the big ones.

Cordon of arrows and snare (though you'd probably want to fudge the duration) come to mind if you have a nature-themed dungeon.

There's some fun to be had with illusions, walls, Nystul's magic aura, and a few others used non-traditionally.

If you relax the restriction on the spells being able to have an indefinite duration per the spell description in the book you can get some interesting options.

-Illusions like Major Image can make a room seem more dangerous than it really is or hide the real dangers.
-A room with an Antimagic Field or a Globe of Invulnerability is bound to make some characters nervous.
-Pit fall traps that drop you into a pit of Evard's Black Tentacles or any other area damage effect

At my table at least players tend not to question if things like these are permanent dungeon features. Just because RAW there isn't a way, doesn't mean someone didn't find a way. It helps that I tend to rule loosely on whats possible regarding their options too.

Don't think of hallow as a room trap. It makes an entire (small) dungeon become beneficial to the inhabitants. I once had a mummy lord use hallow to give resistance to fire to all inhabitants of its tomb thus counteracting the vulnerability to fire. The players did the obvious thing by pulling out all their fire spells only to find they were not as potent as expected.

6th-level spell programmed illusion lasts "until dispelled" and is absolutely fantastic for this.

Determining that it's an illusion requires physical interaction, or an action to make an Intelligence (Investigation) check. So if you program an illusion that isn't likely to trigger either of those it can really mess with people. The first thing that comes to mind is a rolling-boulder trap, where the boulder is actually an illusion -- most characters will just run away from it, and maybe you can engineer a situation where thy run into a more dangerous area. Another good one might be a pit next to a lever -- you pull the lever and an illusionary bridge spans the pit.

You can also set up situations where the illusion turns out to be real. Like, the first two sets of spinning blades are just illusions. So then somebody walks right into the third set and gets sliced, bad, no save.

I also check learned that major image boosted to 6th level gains an indefinite duration , so that’s another on the list.

teleport circles. these can be permanant, and give one-way trasport to somewhere else. if, for example, the other side is broken with no easy way back, this could be a one-way ticket to the underdark or another continent.

mordenkainen's private sanctum is a great spell- can be permanant, covers up to a 100' cube, blocks all sound, the barrier appears dark and foggy, blocks all divniation sensors, teleports, and planar travel. and you can chose selectively from that list, to for example just get a scrying-proof area that blocks teleports and planar travel. this is a great spell for defeninding an area against magic from outside.

Forbiddance is a ritual that becomes permanent if cast for 30 days (so 30k gp to make permanent), protects up to 40k sq feet up to 30' high. it blocks teleports and portals against a specific type or types of creatures (celestial, fiend, fey, undead, elemental), and deals your choice of 5d10 radient or necrotic damage to any of those who start their turn inside the area. a password can bypass this damage.

for proper trap use, we stack the sanctum with forbiddance and hallow. lets say we have a lich, so inside the area deals necrotic damage to fey and celestials, blocks teleports and scrying, grants energy protection from radiant damage, and there is a teleport circle arrival point in a small room just outside this effect. the teleport circle that sends here belongs to a cult who send live restrained sacrifices to the lich for him to feed their souls to his phylactery (or else he will investigate why he didnt get sent food, and eat a cultist).

for guards and wards, remember it can have two stinking clouds. but mainly its an effect that slows intruders bit not guards, and stacks well with golems defending an area. cant see whats ahead, webs regrew in the the stairs behind, and the illusion covered an otherwise-obvious trapdoor in the floor? oh and the illusion-covered door behind you opened to let a golem out once you moved past it.