What is that clock on?
The clock is on the tower.
   src        edge_attr  dst
0    4               on    5
1    7   to the left of    8
2    8  to the right of    7
3    8  to the right of   13
4   12  to the right of   13
5   12   to the left of   14
6   13   to the left of   12
7   13   to the left of    8
8   14  to the right of   12