Undercellar

The undercellar is a public underground place of rest underneath Baldur's Gate that can be entered through the sewers or the Blushing Mermaid. If you enter through the Blushing Mermaid, a guard will talk to you and demand money to walk through the undercellar. He will let you pass whether you pay or not.
In Chapter Five, Quenash will be in one of the undercellar's rooms and is involved in the Searching for Balduran's Helmet side quest. She will give the player a clue to where the helmet is which points to the Helm and Cloak inn in northwest Baldur's Gate.
In Chapter Seven, assassins Slythe and Krystin will engage in dialogue at the center of the crossroads. Krystin will be initially invisible though. The party must obtain the Invitation to Coronation Slythe is holding. This will allow passage into the Ducal Palace. Besides the invitation, the rewards for killing them both are 8000 XP, a letter, the Grave Binder, a Sling +1, the Short Sword of Backstabbing, ten Bullets +1, ten Bullets +2, a Potion of Master Thievery, third level spell scrolls of Clairvoyance, Flame Arrow, Non-Detection, Protection From Normal Missiles, Skull Trap, and Vampiric Touch, a fourth level spell scroll of Monster Summoning I, and