This is a very old postcard, dated 1900, showing a lithograph of the Cave of the Winds at Niagara Falls, New York.
The Cave of the Winds was actually a hollowed out cave behind Bridal Veil Falls on the American side of the Niagara Falls. At the time of this postcard, people could reach the cave by the bridge in the picture and walk behind the falls, experiencing the tremendous roar and strong winds created by the fall of the water.
In the 1920s, a rock slide in the cave made the area unsafe for people to traverse.
Today, a tourist attraction has been created to give this same effect. By a series of redwood decks, bridges, walkways, and stairs, one may go right to the foot of Bridal Veil Falls, standing in front rather than behind the falls. A tourist can still experience the winds and roar of the water.