They Paved Paradise (And Put Up A Monsterous Monlithic Sacrifice To Their Demonic Gods)
Gem of Seeing
This finely cut and polished stone is indistinguishable from from an ordinary jewel in appearance. When gazed through, a Gem of Seeing enables the user to see as if she were using a True Seeing spell.
A Gem of Seeing can be used for as much as 30 minutes a day, divided up into periods of minutes or rounds as the user sees fit.
Details are on page 257 of the Dungeon Master’s Guide