Tumulus

The Tumulus was the name given to a massive and mysterious egg-like object buried deep in the Northdark in the 14 century DR.

Location
While much of the Tumulus remained interred in the earth, one end of it emerged in a cavern situated some east of Waterdeep and  beneath the surface, in the middledark.

Description
From the curved upper end, it was estimated to be an ovoid structure of solid stone and measuring approximately from end to end. The exposed surface was carved all over with symbols, sigils, glyphs, and signs—all of them meaning 'death' in countless languages, some identified, some not. A number of these carried deadly spells that would kill anyone who even saw them. Many, but not all, have already been discharged, but more could still be active under the earth.

History
While its origin and purpose were unknown, the Tumulus was thought to be older than even the elven realm of Illefarn, and that was founded circa.

Over the ages, by 1372 DR, a few efforts had been undertaken to find an entrance, none of them determined, let alone successful.

Rumors & Legends
The structure was rumored to be cemetery or tomb of some kind, hence its name, but this was unconfirmed.