"Holmes was working somewhere under one of the numerous disguises
and names with which he concealed his own formidable identity.
He had at least five small refuges in different parts of London,
in which he was able to change his personality.
(Black Peter)

That revelation from the pen of Dr Watson continues to strike me
as absolutely astonishing!

It is, also, a real challenge to Sherlockian speculation. While
discussing BLAC, and as a parallel thread to the Disguise of the Day,
I ask readers of the canon to send to the list possible locations that
Sherlock Holmes may have used to disguise himself.