Xylos' Doorstep

As you cast the spell, you can either touch a 3 by 6 ft. or smaller door or a spot just as large on a flat and stable wall.

Door. Upon touching a door, you designate the key required for this spell and connect both, creating a silver strand on the ethereal plane. If the key is already connected to another door, the previous silver strand is severed, destroying the connection. The door portrays a large sigil, matching your own description but vaguely resembling a key, in any colour you like. If you touch that door with the designated key, you can choose any active keyhole sigil matching this key and instantly connect both. A copy of that door then appears at the target keyhole sigil if there is space for it - otherwise it fails. The door lasts for 1 minute or until the key, the door or the wall of the keyhole sigil is destroyed and has an arcane lock securing it. Using your key you can unlock the door and anyone may step through either side, appearing on the other as if leaving or entering an adjacent room.

Wall. When you first touch a suitable spot on a wall at least 5 ft. away from any other instance of this spell with a key that is already bound to a door, you create a large active sigil, matching your own description but vaguely resembling the suiting keyhole to the key sigil of the key in use, in the same colour of that key sigil. The sigil remains active for 48 hours, during which you can create a door from the key sigil to it. Upon first creating the keyhole sigil and each subsequent time you touch it again when casting this spell, you can choose to create a door to the key sigil. Doing so refreshes the time it remains active and makes it permanently active if it has continuously been active for one year. This door functions the same way as when created from the key sigil.

Eventhough only one key sigil can be connected to keyhole sigils, the person owning its key can create a copy of that key which allows use of that key sigil and its keyhole sigils. However, only one keyhole can have a door leading to the key sigil at a time. If all keys to a key sigil are destroyed or lose connection, the related keyhole sigils disappear. If a spell or other magical effect that prevents planar travel or nullifies magic affects a sigil, the sigil can't be used. Anything inside the doorframe when the door vanishes is harmlessly launched back to the side they entered from. Casting dispel magic on a keyhole sigil deactivates it. It is up to your DM whether sigils allow transportation between planes.

This spell was created by Trenn Xylos, a self-isolated Conjurer who had many permanent sigils in the significant cities in his realm connected to his living room for ease of gathering materials, food or simply not needing to leave his home often. Because he was frequently helping a group of adventurers traverse - to return a good friend the group had helped a favor - an institute he once worked with took notice eventually and fulfilled their duty as distributors of knowledge. The formula for this spell has since been sought after and most keyhole sigils found are either physically blocked off, destroyed, deactivated or watched.