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.
Otto apparently also printed a copy for the American Post Card Co. Here the Nowell logo is still visible.
There is also an Image 37 (37 - Seattle Water Front) showing the Seattle waterfront. Reuse of image numbers and different image series make it difficult to know how many images Otto published.