*blush*
Yours truly, Mr. "How Come Nobody Reads the Links," missed the link at the top of Raoul's post, which leads to a much wider photo than Raoul showed, and the official text accompanying it. This is indeed a "bridge" over a gap.
The further evidence of lava tubes is encouraging for those of us who support using intact tubes as ready-made shelters from radiation and other hazards. Simple pressurized inflatables would be suitable for long-term stays if enclosed in such a space. On the Moon, too.