It's a fantasy role-playing game.

DM: You are Caleb Widogast, a human wizard . You are the member of the famous group of adventurers. Previously, They get into the rowboat, Fjord and Jester swimming alongside and Nott trying unsuccessfully to hide from them before they leave. you turns Frumpkin into an octopus and throws him into the water.
DM: Okay. So, there is a circular pipe entrance or a tunnel entrance 40 feet down, right as the water gets darker and more murky. Bits of clustered seaweed begin to come up and tickle the bottoms of Frumpkin's tentacles in that vicinity. Elements of it are blocking the front, but you can clearly see there is a dark tunnel that continues into the earth, beneath the city, beneath the docks. You don't know how far it goes, necessarily.
Player: Do Frumpkin and I see anything alive or moving down here?
DM: Make a perception check.
Player: Pretty good. 18.
DM: You do not see anything alive or moving in this vicinity. Best you can see, the tunnel continues in for about 15 or so feet, and there is a metal grate. You can see eight or so bars across. Actually, about ten bars, about an inch thick each, and they're horizontal, though it's a little bit tilted to one side.
Player: How far apart are each of the bars?
DM: With eight of them and it's about four and a half, five feet across. Sorry, ten across. It would be about six inches between each.
Player: I think my octopus could probably squeeze through that.
DM: Yeah, your octopus could.
Player: (plopping sound)
DM: All right.
