The first step is to discover that all of the cities are home to IPV4 DNS root servers. The interactive map at http://www.root-servers.org/ can be used to find server information. For example, Quezon City hosts a DNS root server at 192.58.128.30.

The next step (still using Quezon City as an example) is to apply the indexing instructions "4(4+1)_(1-6)(1-6)3" to the root server ip address. Taking it as "digit 4, digit 4 + digit 1, digit 1 - digit 6, digit 1 - digit 6, digit 3" gives 5, 6, 0, 0, 2 for room 56-002.

Upon going to building 56 and visiting room 56-002, the solver will see a marked pipe exiting the room. That pipe continues on to one of the non-numbered rooms, in this case room 16-065 corresponding to Fussa. The marker on the pipe end in 56-002 indicates the subway lines (on the map) used to connect the two cities. In this case the list is red, blue, orange, pink, red.

Tracing out a route between Quezon City and Fussa on the subway map by following those five colored lines in order draws the letter O.

The full set of data: