The old cellar?

From Spurgeon's sermon, "The Prodigal's Return"

When the 'light' of God's grace comes into a person's heart,
it is something like the opening of the windows of an
old cellar that has been shut up for many days.

Down in that cellar, which has not been opened for many
months, are all kinds of loathsome creatures, and a few sickly
plants blanched by the darkness. The walls are dark and damp
with the trail of reptiles; it is a horrid filthy place, in which no one
would willingly enter.

You may walk there in the 'dark' very securely, and except now
and then for the touch of some slimy creature, you would not
believe the place was so bad and filthy.

But once open those shutters, clean a pane of glass,
let a little light in, and now see how a thousand noxious
things have made this place their habitation.

Surely, it was not the 'light' that made this place so horrible,
but it was the light that showed how horrible it really was!

So let God's grace just open a window and let the light into a
man's soul, and he will stand astonished to see sinful he really is.