Mysterious burial chamber with rich interior (7)
I believe the answer is:
cryptic
'mysterious' is the definition.
(I know that mysterious can be written as cryptic)
'burial chamber with rich interior' is the wordplay.
'burial chamber' becomes 'crypt' (crypt is a kind of burial chamber).
'with' says to put letters next to each other.
'interior' indicates the central letters.
The central letters of 'rich' are 'ic'.
'crypt'+'ic'='CRYPTIC'
(Other definitions for cryptic that I've seen before include "Mysteriously obscure" , "'Obscure, puzzling (7)'" , "(Of crossword) withindirect clues" , "Type of crossword clue (but not this one!)" , "Concealing meaning in puzzling way as Crosaire does" .)