
The little human-sized buildings along Fort Pitt Boulevard originally faced the Monongahela Wharf, where the steamboats lined up.

When Amtrak stopped using this bridge and the downtown tunnel into which it led, the Port Authority seized the opportunity. The bridge now carries the streetcars over the Mon and into the subway, the first part of which uses that old railroad tunnel—so that, like many other things in Pittsburgh, our subway is cobbled together from spare parts.
From Station Square across the river into the subway tunnel. You can also download a full-resolution version from the Wikimedia Commons file page.