The password to enter the door in the SE tower of the 1st level is "SNOOPCHERI". Use the rotten cheese on the mousehole. Some small help for playing the game successfully: When you create your characters, it may be a good idea just to make all of them Dracons.
This is untested, but unless you have at least one of this fire breathing race you surely wont survive the game. So maybe it would be good to have more. Use a good mix of the classes, try to take one of each spell class and a good solid thief that is at full strength. Get a good enough thief and you dont need a fighter. It may be slow, but keep rolling till you get the best character possible. Be sure to make at least one character female, there are places in the game where this is a must. Don't do it and be sorry later! Diversify your skills.
Have each character specialise in a few skills relative to his class. Do not worry about developing weapons skills, you have no use for them if you created your party correctly. In fights early in the game use DRACONS BREATH ATTACK, just be careful not to over extend yourself. Rest after each encounter, backing up your hard work. Always search the area after a combat. Search each square you step in. Not only this, but search facing all four directions, many things can only be found that way. Thieves are not always true. If you find a lock and have your thief open it, allways guess it is poison unless you are 100% sure (I.E. tried it before) because it is better to suffer something else than to die by getting this wrong. Don't bash doors early in the game! If your characters are not very strong you will be sorry. Jammed doors do you no good, as you might never be able to open them again. Same goes for picking the lock. Wait till you get a caster capable of conjuring knock knock with at least 18 points (prefereably 24) and do it this way. It is much more sure. Once you know there are secret panels or buttons, keep walking past them until you discover them. You can find them by looking at the maps and know where they are, sometimes it takes awhile to sense them.