Charlie stepped into the narrow elevator with Bruce following close behind.

The control panel in the elevator only had one green button. Bruce pressed the button and explained, "If someone is at the bottom, press this button to go up. If someone is at the top, press this button to go down. You can't stop in the middle."

Charlie nodded. As the elevator started moving down, he looked at Bruce and asked, "How deep is it down here?"

"60 meters," Bruce answered.

Charlie asked curiously, "How