How do you get into taverly dungeon in runescape

If you are talking about the bit the leads into the Dragons area, you will need a dusty Key, one of these can be obtained by going to the Room Full of Black Knights then On the East side of this room is a Jail Cell. To enter you must kill the guard outside, take the key he drops and use it with the door. Once inside you can talk to the Explorer who is locked inside and get the Dusty Key.