Ruby, 2 lines, 92.16% speed
\ndef dest_city(paths)\n    path_hash = paths.to_h\n    (path_hash.values - path_hash.keys).first\nend\n
```\ndef dest_city(paths)\n    path_hash = paths.to_h\n    (path_hash.values - path_hash.keys).first\nend\n```
['Ruby']