D&D 5E What are the best ways to conceal an entrance/door with or without magic?

[Shrapp Hamnier]

(Formerly titled "lich bat-cave")

I am making one of the ultimate bosses for my party to fight; a lich with an enormous hidden lair under a city. The problem is he needs it to BE ENORMOUS! He is storing hundreds if not thousands of corpses (including one of a dragon) in order to use for an undead army (I've already handled the issue of only being able to have so many undead at a time due to spell slot restrictions).

My question is, what is the best way to hide this giant cavern, and the rest of his lair for that matter. It will have 3 parts, the main area for most of his studies (connected to a house in the city), the giant cavern area (where he hides the bodies and does more dangerous experiments), and a small room where he keeps his phylactery). Each of these 3 sections are to be concieled (he is super paranoid, it would take way too long to REALLY explain why his lair is under a city rather than in the middle of nowhere).


Edit: I'm asking about the DOORS for these three main areas. How do I conceal them (with or without magic, but preferably with since it's a lich)? This is my second time as a DM, and the first time making my own boss lair that uses magic (I don't really even know how to lay magic traps, though I am having an easier time finding information about those).

 

[Ancalagon]

Undead don't have to stretch or have personal space issues, so you can pack hundreds of endlessly patient undead in not too big a room.

The best way to hide would be for the rooms to be simply sealed off, only accessible via magic. Even better, each "room" is a small chamber with a hidden portal to a demi plane.

Incidentally, I initially believed that you were running a game where Batman was a lich.

 

[Jester David]

Could just be beneath the sewers. Not many people venture into dark caves. It's not like people explore sewers for fun.

 

[Dannyalcatraz]

Humanity has been building cities on top of cities- and even paving over natural features like caves and rivers- for centuries. His lair could be not so much a cave as a portion of an older settlement that has literally been overbuilt. The same works for a paved over river.

A similar scenario works for cities over caves- and remember, there could be different ramifications if the city planners knew about the caves or not

http://weburbanist.com/2007/10/15/7-more-underground-wonders-of-the-world-lost-caverns-and-cities/



http://environment.nationalgeograph...d-rivers-nyc-sunswick-creek_46402_600x450.jpg

http://la.curbed.com/2013/8/15/1020...los-angeles-river-before-it-was-paved-in-1938

http://www.nytimes.com/2009/07/17/world/asia/17daylight.html?_r=0

http://welovebudapest.com/budapest.and.hungary/underground.adventure.roundup.of.caves.in.budapest

 

[Shrapp Hamnier]

I like the cave idea, as well as the small rooms of demiplanes. But my poorly asked question is more about the doors. (I'll make an edit in the OP specifying that). I want to know how to hide the entrances so they CAN be found, but with increasing difficulty to bring out the detective in my players.

This will be my first time DMing where I have made a lot of stuff from scratch. I can make dungeons and castles and any other normal layout all day (or week), and I know how to do combat and support magic. But I know nothing of setting up latent magic, such as how to conceal a door or even lay magic traps and wards. Finding them I can do, but I don't want to set anything up that a player couldn't hypothetically do, at least not without a good explanation of why they can't. (Not that I feel a need to explain every minute detail, but I don't want my NPCs to be able to do things "because they can")

 

[Li Shenron]

(Formerly titled "lich bat-cave")

I am making one of the ultimate bosses for my party to fight; a lich with an enormous hidden lair under a city. The problem is he needs it to BE ENORMOUS! He is storing hundreds if not thousands of corpses (including one of a dragon) in order to use for an undead army (I've already handled the issue of only being able to have so many undead at a time due to spell slot restrictions).

My question is, what is the best way to hide this giant cavern, and the rest of his lair for that matter. It will have 3 parts, the main area for most of his studies (connected to a house in the city), the giant cavern area (where he hides the bodies and does more dangerous experiments), and a small room where he keeps his phylactery). Each of these 3 sections are to be concieled (he is super paranoid, it would take way too long to REALLY explain why his lair is under a city rather than in the middle of nowhere).


Edit: I'm asking about the DOORS for these three main areas. How do I conceal them (with or without magic, but preferably with since it's a lich)? This is my second time as a DM, and the first time making my own boss lair that uses magic (I don't really even know how to lay magic traps, though I am having an easier time finding information about those).

To conceal the entrance from the player characters?

A very visible door with a "welcome" mat and a grin on the DM's face

 

[Sadras]

I like the cave idea, as well as the small rooms of demiplanes. But my poorly asked question is more about the doors.

A wall-hanging rug conceals a passageway.
A large colourful aquarium (on wheels) camouflages a door behind it, which is painted the same colour as the cavern.
There is always the old statue/library mechanism which opens up a secret passageway. Perhaps the book's title provides a clue to it (the book) being a lever.
The old hidden trapdoor under the carpet.
Rungs 'beautify' a cavern from floor to the ceiling - at first glance most assume these are part of the décor. One of these rungs is actually the handle of a hidden door which is almost impossible to identify from the ground. The PCs need to climb some before the door becomes more noticeable.
...etc

 

[Imaculata]

To dig an entire underground lair in secret, would be rather difficult. So I would always assume the Lich used an already existing underground structure, and expanded it. The most logical location would be a system of catacombs, since they provide the Lich with ample materials to build his army. Plus it is already a maze, so all he needs to do, is hide the entrances, and add traps. So how would the entrances to such an underground lair be hidden?

The lair may still have some connection to the surface. In the case of catacombs, it may be connected to a single ancient tomb in a graveyard, that is now closed off. It may also be connected to an old church/cathedral, or the sewers. The simplest way to hide these entrances, would be to simply collapse the tunnels. The lich may leave one entrance for him to use, in case he wants to visit the surface. And such an entrance could be hidden with a hidden switch. Maybe there's a mural in an old haunted cathedral, which has a hidden button that opens the entrance to the Lich's lair. You yourself described that he has a house in the city that connects to the lair. Well, why not simply have a good old sliding wall, with a hidden switch? I don't think a clever Lich should hide his surface entrance with magic, since magic can be detected, and would draw attention to the house if anyone was looking for it. But if there is nothing remarkable about the house, and there is not a trace of magic, no one suspects a thing.

The place where the phylactery is stored, would be the most hidden of all. This is the most important room for any Lich, and thus it would be hidden both mechanically and magically. There would also be plenty of traps, and he may keep a fake phylactery somewhere more easily to access. Everything relies on his phylactery being kept safe. So it would be deep down in his lair, well hidden, well trapped, and heavily guarded. There would be plenty of illusions and magical protections as well. And of course alarm spells.

The caves would not need to be hidden all that much. All that matters to the Lich, is that any direct connections to the surface have been collapsed. If he uses this area often, then he would need quick access to it. A complex metal door would do the trick, to which only he has the keys. He may use illusions to misdirect intruders, and lead them down trapped passages that are all dead ends.

 

[Quartz]

Consider a real-world sink hole. Make sure the top is covered by a few feet of stuff, reinforced underneath, and you're done. Perhaps topside is a city park endowed by the lich so that no one builds on it. More fantastical would be a magic everlasting ice rink - the feet of ice being the cap on the sink hole.

Entry and exit could be by Teleport or Phase Door for when the lich wants discretion, or by Earthquake, Disintegrate, or simply by the dragon bursting through when impressiveness is required.

 

[Uchawi]

You could treat magic as physics, where once a portal or physical property is established it can not longer be detected as magic. For example, using mirrors as a portal when one mirror is reflected against an opposite mirror. An alignment of objects like Stonehenge, or considering modern examples like Washington DC, specific alignment of buildings and streets to create a focus to another plane. As to lairs, you could allow the litch to rule both the roof tops and attics via tight ropes, clothes lines, or similar mechanism. The litch may also travel underneath buildings via crawl spaces or cellars, and then there is always sewers. The corpses can be hidden in plane sight behind walls, underneath floors, in ceilings, or within statues or other objects.