Why an Okinawan turtle shell tomb* in MIT? That was my first impression when I saw this mysterious structure. Of course, there is no way such an indigenous structure (with a little Western twist) is in a traffic median in the middle of Cambridge. So I aborted the idea soon.
*An indigenous style of burial in a southern island of Japan. The tombstone resembles to the shape of a turtle shell, and does look like an uterus, I admit.
Reference: Turtle shell tomb (Kikkobaka), from Wikipedia
After a closer look, I realized it's the Redline tunnel portal leads to the Longfellow Bridge. Funny, I've been through the tunnel many many times. But I always got carried away by the river view and the Liberty Hotel, and didn't even imagine how the tunnel portal looked like; only train operators can see it.
There is not much information available about the Cambridge Tunnel. The Red Line began its operation between Harvard and downtown Boston in 1912. If the railroad was totally new and hadn't been used by other railway services, the tunnel must have been built around that time. It sounds like a good material to be registered for historical significance, but I guess people are not so keen on the cement finish.
I know, I know. It's not curved stone or brick, but it's little sad to see crumbling. Because I like a little effort of decorating the portal with Corinthian (?) motifs. Wait, wait, it's not going to cave in soon, right? Only the facade is crumbling but structurally, it's all right, right?
Locate Cambridge Tunnel @ Google Map
Cambridge Tunnel, Structurae: http://en.structurae.de/structures/data/index.cfm?id=s0021994