The Collaborative International Dictionary of English v.0.48:

Penetralia \Pen`e*tra"li*a\, n. pl. [L., fr. penetralis
   penetrating, internal. See Penetrate.]
   1. The recesses, or innermost parts, of any thing or place,
      especially of a temple or palace.
      [1913 Webster]

   2. Hidden things or secrets; privacy; sanctuary; as, the
      sacred penetralia of the home.
      [1913 Webster] Penetrance

WordNet (r) 3.0 (2006):

penetralia
    n 1: the innermost parts