From Ferrus (3)

"" is an Series: in. As its name suggests, it is the third ST: from ST:.

Location and Uses
"ST:" can be collected from any ST: after ST: has completed the ST:, provided he has collected the first and second NaN Letters from ST:, fulfilled both of ST:'s ST: requests, and then entered the ST:. Once again, the ST: includes a photo—this time of a location near a ST: in a wooded area of the ST:—and a request from ST: for ST: to meet him there. It reads,

The location in the photo can be deduced as the NaN Spirit Tracks (Object)s due south of the ST:. ST: can drive the ST: there to meet with ST:, who gives the young engineer a valuable ST: that he found while exploring the ST:.