Sewer Token

Wondrous item, rare

This copper coin is embossed with rats walking around its edge. On either side is a matching radial pattern. You can use an action to speak the coin's command word and toss it onto the ground in a 5-foot-square space that you can see within 20 feet of you. When it lands, a 3-foot diameter tunnel appears in the middle of the space and extends downward up to 20 feet, complete with an affixed ladder. The tunnel ends early if it reaches an open area, and the ladder descends down up to 10 feet into the new area. The tunnel does not compromise any structural integrity when it appears.

The coin also expands, growing to fit the size of the tunnel's entrance; the coin then becomes the cover for the tunnel and weighs 20 pounds. The tunnel remains for 1 hour or until you use an action to speak the coin's command word again within 30 feet of it. The cover opens only at your command, which you can speak as a bonus action, although anyone can close it again. It is immune to the knock spell and similar magic, such as that of a chime of opening, but a creature can forcibly open it by succeeding on a DC 25 Strength (Athletics) check using an action. The cover closes itself after 1 minute if left open. A creature that's in the tunnel when it disappears is safely ejected from the top of it.

If the space where the tunnel appears is occupied by a Medium or smaller creature, that creature must also make a DC 15 Dexterity saving throw. On a failed save, the creature falls down into the tunnel. On a successful save, the creature remains in the space but doesn't fall in.

When the tunnel disappears, the cover returns to its coin form. If the tunnel reached an open area below it, the coin falls into that area before the tunnel disappears at the end of duration; otherwise, the coin remains on the surface on which it landed. Speaking the command word to end the effect early allows you to choose whether the coin drops into the tunnel or remains on the surface.

Once the coin creates a tunnel in this way, it can't do so again until the next dawn.

Day...six? ten? The Prince couldn't be sure.
He was, however, sure that his prison had been part of the sewers once. He could even hear water running beyond the brick walls, but every entrance to the room been sealed with stone and mortar. He'd tried every way he could think to find help and escape, but the room was sealed in absolution.
The mystery that plagued him was the rumbling. Once in a while, there would be a thud, followed by a wobbling groan, before an entrance from above would open. Then food or other necessities would be thrown down, and the hole would vanish again; whoever stood at the top cared little for his pleas. It was never in the same place twice, and the ceiling was far too high for him to reach the opening.
He knew the sound from the day he'd fallen in here, but never what made it, or who.
He had the time to think, at least.