Boltstrike Pillar is a massive stone column that twists and
turns seven stories into the air. The tower has been a node of
supernatural forces for ages. It may have started as a moreor-
less natural formation, but over the centuries it has been
partially hollowed out and carved into living spaces and magical
workshops. Around the tower is a walled area with a few stone
and timber dwellings and storage structures, a well, etc. Other
features of the living space outside the wall depend on which
icon holds power.    -p. 301, 13th Age Core Book

Boltstrike Pillar appears in Chapter 10, the “Blood and Lightning” adventure in the 13th Age core book.  Below is the rough draft and a bonus sketch for a different adventure that Rob was toying with at the time.