Simon the Coward fell in love with a Guildmaster's niece but was told he could not court her unless he brought the Guildmaster three cave pearls. Cave pearls only being found in infested catacombs, this was an impossible task. But, smitten, Simon acquired all the silver and mithril wire he could and wove it into a crude half-dome of mesh and had it blessed by 3 different holy men. It was crafted so he could carry it over him with a stick and he went in and out of the caves unmolested and found three cave pearls and courted the fair niece.
It's impossible to climb a ladder while under this cage, impossible to swim, barely manageable to traverse stairs, but while under it, no one will notice you exist unless you hurt them (provides Sanctuary).