1

It is triangular

2

It is an unusual shape

3

It is built into a clock

4

It is made from Resolve: {fungi|energy|webbing|canvas|paper}

5

it slides into the ceiling

6

it slides to the side

7

it has a talking face

8

it is incorporated into a larger piece of art

9

it is trapped and nearby is a secret door that goes to the same place

10

It is intelligent

11

it is a mimic or other shapeshifter It has a hidden compartment with something valuable inside

12

It opens to somewhere unexpected - Resolve: {a cliff face|a chasm|water|darkness}

13

It is a magical portal

14

It contains an imprisoned spirit

15

It drains energy from any who touch it

16

The door makes sounds

17

It has a book case built into it

18

It is covered in bloodstains

19

The door is sticky