Atlas Obscura describes the collection, including its most famous object, the “necropants” …

The museum focuses on the elaborate and esoteric spells and rituals that the regional magic called for which would provide such effects as conjuring a creature to steal goat’s milk or making someone invisible. The collection features a number of artfully displayed original artifacts and entertaining replicas such as rune-carved pieces of wood, animal skulls, and a number of Icelandic magical staves. However, the most shocking and remarkable piece is easily the so-called “necropants” which is the dried skin of a man from the waist down. These horrifying leggings were used in a spell that would supposedly bring the caster more money.

The necropants are such a big deal that they have their own separate article on Atlas Obscura, which provides a more detailed description and more historical context:

These vile leggings were the main component in a ritual that was said to bring the caster unlimited wealth, although the requirements of the spell were so outlandish that simple back-breaking labor seems like a more attractive alternative.

According to the ritual, to create a pair of necropants, the sorcerer must first make a pact with a friend, stating that once the friend has died of natural causes, the sorcerer has permission to skin them from the waist down. Once the friend is dead, the greedy magician must then wait until the friend has been buried, dig up the body, and then skin the lower half of the corpse without creating any holes or tears, thus creating a pair of gruesome skin pants.

Once the “necropants” have been created, the caster must don the purloined pantaloons against his bare skin. Now the ritual requires that the sorcerer steal a coin from a destitute widow, and place it in the empty scrotum of the pants along with the magical Icelandic stave (symbol), Nábrókarstafur, written on a scrap of parchment. And that’s it!

The pants soon become indistinguishable from the wearer’s body, and so long as the original coin was not removed, the scrotum should continue to miraculously fill with coins for the rest of time.