Dolblunde was a gnomish city located in the Underdark beneath the Sword Coast North. It was abandoned as of the mid-to-late 14th century DR, and had become the lair of Daurgothoth, a mighty black dracolich known as the “Creeping Doom”.

Dolblunde was located in the upper Northdark under the hills about 42 miles northeast of Waterdeep.

While it was deep underground, it was not as deep as many other Underdark settlements, allowing it to maintain a connection with the surface. It could be accessed via the deepest depths of Undermountain and by the so-called “Bandit Tunnels” from Maiden's Tomb Tor.

It lay along the same underground route that led further down to the mind flayer city of Ch'Chitl.

There was also a water- and mud-filled tunnel at the bottom of the River Dessarin that the dracolich Daurgothoth used to enter and leave Dolblunde unobserved.

Lastly, the city was said to have at least one nexus point for the Trail of Mists, an ancient means of connecting gnomish settlements via the Ethereal plane.

https://forgottenrealms.fandom.com/wiki/Dolblunde