Old tomb quiet with myriad bats (7)
I believe the answer is:
pyramid
'old tomb' is the definition.
(I've seen this before)
'quiet with myriad bats' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'with' means one lot of letters go next to another.
'bats' is an anagram indicator (slang for mad).
'myriad' is an anagram of 'yramid'.
'p'+'yramid'='PYRAMID'
(Other definitions for pyramid that I've seen before include "Polyhedron, one face a polygon, the rest triangles with common vertex" , "Egyptian edifice" , "A 3D shape" , "type of selling" , "Solid figure with triangular sides" .)