This word is pronounced gooEEshay (or GWEEshay if you're not being quite so French).
A guichet is a small opening in a wall, a sort of hatch, but particularly the window of a ticket office.
Photo of Nanpingbei Station by SCJiang. It's in China, but you wouldn't know it, would you?
Receptionists sometimes hide behind them.
The important thing with a guichet is to look through it to see what sort of a calendar is on the wall.
Few things in the world are more revealing of character.
Spot the Frippet: guichet. This word is French, as I said. Before that it came from a Germanic language. The English word wicket came along a similar route from a similar source.