Just off the road a man lies dead, pierced through the heart from behind by an expertly thrown and ornate dagger which remains in the body. A long strip of cloth torn from the man's shirt has been tied around his neck; on the tag end an unknown hand has written a cryptic inscription: "For Djaygo."
When you get to the next town, everyone is talking about a mercenary woman found slain in exactly the same fashion in her room at the inn where she was staying.
A nifty little encounter appropriate for any powerful sorcerer/magically adept monsters lair.
When the party have penetrated to an appropriatly impressive level/room they encounter The Door, this door is a vessel through which the Sorcerer/Monster can safely work against any intruders, the door is heavy duty iron bound studded oak wrought with craft skill and magic, set in the middle is a crystal orb, once the party get within a preset distance the orb flickers briefly as the door warns its "master" of the intruders, the master can then effectivly possess the door itself, this means that all movement the door is capable of (i.e. opening and closing) come under the control of the master, the master can also cast spells from the door as if he were there himself, all the while any damage that is inflicted in return merely damages the door, this will in effect ruin any of the parties chances of surprise, allow the master to assess the parties abilities while remaining safe and sound and finally will probably cause the party to waste some of their juicier items/spells on a chunk of wood and iron, and if the master happens to have a deadly spell or three it could also reduce the size of the party,
Of course if you wanted to be really nasty you could have the door open to admit one person and then slam shut on the second person (squish) whilst blasting away with every spell in the mastrs repetoir