This narrow entrance to a teahouse is called "Nijiri-gutchi" and is provided to symbolize the mental preparedness of the guest who enters into an undefiled tea ceremony room.
In order to enter into a tea ceremony room through this small opening, a guest must bend ("nijiru") her or his knees and crawl on her or his hands and knees like a baby.
A guest enters into a tea ceremony room as a genuine and innocent human without any impure and worldly belongings such as swords, luxurious garments, social status, gender and so on.
When a guest squeezes through this restricted
entrance, she or he has to remove her or his superficial and mundane properties to get rid of any hindrance.
According to the philosophy of the tea ceremony, a teahouse is a small and pure utopia on the earth.
You can enter here through this narrow gate as a sincere and pure human and be wholeheartedly treated as a true guest of honor by the master at a tea ceremony as if it were an once-in-a-lifetime opportunity or "itchigo-itchie."