
From Wikipedia:
The Lewis and Clark Centennial Exposition … was a worldwide exposition held in Portland, Oregon, United States in 1905 to celebrate the centennial of the Lewis and Clark Expedition.
The above is a hand-tinted photograph of the expo grounds, which was located on a former marsh/lake called Guild’s Lake (pronounced ‘guile’) in industrial northwest Portland. The only remaining building is the home on the bottom right, which you can see on Google Streetview.
This is a map of the expo grounds [high rez]:

And here’s a photo of the U.S. Government Building in the distance on the peninsula in the middle of the lake:

Sadly, the beautiful buildings were only meant to be temporary and are now long gone. As is the lake.
Photos and info via Vintage Portland and Oregon Encyclopedia