Echolost

Where no tunnels reach, there can be found the closed cavern of Echolost.  Vast in size, echoes chase each other across the wide space for eternity.  Some are so complex that they may be considered creatures in their own right, though they could not exist outside the space of Echolost.  One side of the cavern in particular, known as the Wall of Echoes, is special.  It appears as a flat black expanse of dense, rock-like material.  It absorbs any sound that falls upon it, then once again emits that sound minutes, hours, days, or sometimes many years later.  Sages sometimes come here just to listen to the wall, hoping to hear whispers of knowledge long lost.  The other major feature of the cavern, the Earthpool, is a basin of dust so fine that it appears to be liquid, though woe to those who mistake the pale dust for water.

Once first-time visitors (or or those returning after more than a year) clear the site, on subsequent visits the chance of encounter is drastically reduced.

Abilities

• Base - Visitors gain a +2 bonus on saving throws made while in a subterranean environment (or while on the Earth Plane).  Furthermore, they gain a +1 bonus on any hide, move silently, search, and spot checks while in a subterranean environment or on the Elemental Plane of Earth.

• Higher Order (5 uses until recharge) - Once per day for a period of 1 minute per character level, you gain the ability to burrow through dirt at a speed of 20 feet and through rock at a speed of 5 feet.  You cannot charge or run while burrowing.  You do not leave behind tunnels that other creatures can use because the material you tunnel through fills in behind you, but you can bring one other creature with you ahead of the fill whose size is equal to or smaller than your own
  

Reharge Condition - Chisel a stone from the Wall of Echoes