Friday Photo: What is this thing in downtown Saint Paul?

While I was looking at old aerial photos of Saint Paul for the Then & Now yesterday, I kept noticing this large series of structures just East of the state capitol complex.

1957-mystery

The picture is from 1957. Does anyone know what this is?

Bill Lindeke

About Bill Lindeke

Pronouns: he/him

Bill Lindeke has writing blogging about sidewalks and cities since 2005, ever since he read Jane Jacobs. He is a lecturer in Urban Studies at the University of Minnesota Geography Department, the Cityscape columnist at Minnpost, and has written multiple books on local urban history. He was born in Minneapolis, but has spent most of his time in St Paul. Check out Twitter @BillLindeke or on Facebook.