Maintenance of some sort. I know some older planes had tunnels in their wings that would allow crew access to the engines. However I think the scale on this photo is off though.

There should still be engine where he's standing and even with a tunnel there wouldn't be enough room for him to stand.

WVOtoGO will probably know.

__________________
1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
1990 300SEL Smoke Silver (Parting out)
1991 350SDL Blackberry Metallic (481)

"The thing is Bob, its not that I'm lazy...its that I just don't care."