The waterway had only an entrance, no exit.
Having wandered through the water channel for some time, Xiao Ling and Yu Guangnan had carefully trudged every inch, only to discover at the end that it was a dead end; to exit, they would have to first backtrack.
Of course, there was the option of drilling a hole from above, but they were unclear what lay directly above them; rashly boring a hole might result in them being buried.
However, this also appeared to be the best option at the moment, as long as they found a suitable spot.
The tourist map showed the layout of the buildings above ground, and picking an open spot would allow them to emerge.
But the layout was only approximate; the safest bet was to find a larger venue to ensure they wouldn't hit any of the building's support structures.