What is under the bridge?
The stairs are under the bridge.
    src        edge_attr  dst
0     0               of    6
1     0   to the left of    8
2     2               of    6
3     2   to the left of    4
4     3  to the right of    8
5     3   to the left of    4
6     4  to the right of    3
7     4  to the right of    2
8     4  to the right of    6
9     4            below    5
10    4            under    5
11    5            above    4
12    6   to the left of    4
13    8   to the left of    3
14    8  to the right of    0
15    8               of    6
16    9               of    6