Crypt of the Ancients

The Crypt of the Ancients is an outlying tomb of the Drowned Temple, located in the Festering Woods. The nephalem set traps within the tomb, which caused the deaths of at least one group of tomb robbers.

Later, Alaric sent The Nephalem here to gather one of two keys, in order to gain access to the temple.

In-game
The crypt is a dungeon in the Festering Woods in Act I of Diablo III. A Rare elite skeleton is always found inside.

In the quest "The Broken Blade," The Nephalem must visit it on their way to Drowned Temple in order to recover one of the two beacons. If Lyndon is present, he will comically tell player to give the relic to him for "safekeeping".

The beacon is in the north-eastern corner. The southern section contains a and the Tomb Robber's Journal.

Trivia

 * Due to guaranteed elite pack, small size and availability this location (along with the Warrior's Rest) was widely used for farming in early versions of the game, until it was nerfed heavily.