Wondrous item, very rare
This large parasol is made from fine black silk and feels eerily cold to the touch. When you open the parasol, it sheds darkness in a 5-foot circle directly beneath it. If you speak its command word as an action, the opened parasol stands upright in an unoccupied space adjacent to you, and the darkness it sheds becomes a portal to a demiplane. Speaking the command word again closes the portal. Any creature that steps into the portal is immediately transported to the parasol’s demiplane, which appears as an endless black void, though the demiplane extends for only 30 feet in any direction. While creatures and objects within the demiplane are starkly visible against its impenetrable blackness, light sources fail to illuminate the demiplane itself. The atmosphere inside the demiplane is breathable air. While the portal to the demiplane remains open, the parasol is visible in the center of the demiplane, and a creature can return to the Material Plane by touching the parasol as a bonus action. The parasol can’t be moved on either the Material Plane or within its demiplane while the portal is open. You can speak the command word to close the portal while inside the demiplane. If closed in this manner, the portal can only be reopened from the Material Plane.