If you go where the tour guide is and go to the right there's garbage cans there
They are in one of the two trash cans near the Tour entrance (under the garbage).
The one with the tickets is the second of the two round cans to the right.
Look in the round trash cans to the right of the Tour entrance. Move the trash out of the way until you find the tickets.
In one of the round garbage cans beside the underground tunnel's gate. You have to dig through some garbage before you can find the tickets. After that take them to the old man in the Internet cafe. (If he doesn't pay attention, take a green balloon from the Clown Store to the kid in the Country Side, then try again.)
There are 2 tickets at the bottom of one of the two large trash cans to the right of the Underground Tour entrance. (Dig down to the bottom.) (see related question)
you find the tickets in the two garbage cans next to where you will go into the tour. pick the one that is open. than it is all the way at the bottom. so you will have to move it with your mouse.
If you have the Underground Tour tickets, go to the Internet Cafe on Main Street and return them. If you don't have them yet, they are in one of the two large trash cans by the Tour entrance.
You can find two tickets to the sold-out Underground Tour : they are in the second of two round garbage cans to the right of the Tour entrance (dig away the trash). You cannot use them, because they are not yours. You need to return them to the owner, who is in the Web Browser Cafe on Main Street. (It may help if you first take a green balloon from the Clown Store to the little boy in the Countryside.) (see related question)
There are two tickets to the sold-out Underground Tour in one of the round trash cans by the tour entrance (the one closer to the Cafe). Dig down through the trash to find them, and return them to their owner at the Web Browser cafe on Main Street. (see related question)
There are two tickets to the Underground Tour in the second of the pair of trash cans to the right of the entrance. But you can't use them because they aren't yours. Once you have taken a green balloon to the boy in the Country Side, you will find the ticket owner at the Internet cafe on Main Street.
You will find two tickets in one of the trash cans near the Tour entrance. You must return them to their proper owner. You will find him in the Internet Cafe on Main Street. (You may have to distract him. See related question.)
There are two round trash cans to the right of the Underground Tour entrance. Dig through the open trashcan (the one on the right) and at the very bottom, you will find a pair of tickets. You cannot use them, however. You must return them to their owner, who is at the Web Browser Internet Cafe. (see related question)