Limpid
Etymology
From Latin "limpidus" ("clear"), possibly related to "lympha" ("water, clear liquid"). It applies to literal transparency and, by extension, to writing or music of untroubled clarity.
adjective · /LIM-pid/
Perfectly clear and transparent — of water, air, eyes, or prose.
What it names
A clarity so complete it seems to have no medium at all — you look straight through to what lies beneath.
Example
The mountain lake was so limpid she could count the stones on the bottom.
Related idea
Pellucid is a close synonym that leans a touch more toward intellectual clarity; limpid keeps a cooler, more sensory calm — clear water rather than a clear argument.