A blindfold is a tool that can be used to achieve temporary blindness. This can be useful if you are about to encounter a monster that can do you harm with its gaze (floating eye, pyrolisk, Medusa) or that can blind you (yellow light).
After gaining intrinsic telepathy by eating a floating eye corpse, applying a blindfold is good for detecting monsters such as that leprechaun who stole your money or those soldier ants you want to avoid.
However, a towel is strictly better than a blindfold, since it also gives temporary blindness when needed, and it has other uses too.
There is a guaranteed blindfold on the first level of Vlad's Tower.
The blindfolding was performed by binding a piece of the
yellowish linen whereof those of the Amahagger who condescended
to wear anything in particular made their dresses tightly round
the eyes. This linen I afterwards discovered was taken from the
tombs, and was not, as I had first supposed, of native
manufacture. The bandage was then knotted at the back of the
head, and finally brought down again and the ends bound under
the chin to prevent its slipping. Ustane was, by the way, also
blindfolded, I do not know why, unless it was from fear that she
should impart the secrets of the route to us.