This is a photo of the 1909 World's Fair held in Seattle, the Alaska Yukon Pacific Exposition. It shows an exhibit hall prior to the opening of the fair, when only Frank Nowell, the official photographer, was allowed to take photos there. Part of Nowell's logo is visible in the lower right corner. Apparently Otto printed the image on contract for the American Post Card Co.
There is another Image 35 (35 - Parade Golden Potlatch Seattle) showing a float in one of Seattle's Potlatch Parades held from 1911 to 1913. Reuse of image numbers and different image series make it difficult to know how many images Otto published.