Weird construction thingy

[ffutures]

Anyone know what this is? It's been on site across the railway for ages and I can't figure it out. You can't see what's under the white tube thingy in this picture, and most of the time it's concealed by the wall, but the glimpses I've had are a rectangular object about six or eight feet high.

Unfortunately they've now closed off the observation grilles on the other side of the railway, not sure why but my guess is health and safety issues, so I can't get a better picture.