The WR SW Plains Line (Chinese: 曠鐵西南曠野綫) is one of the route that Wilds Railway operates. The route connects Chong Shu Chau and Lake City, and acts as one of the important route to access Lake City from other lines e.g. the Elizabeth line.

The route is planned by Navi in early August, 2022, with a initial plan from Spawn to SW Plains. However this plan is quickly abandoned due to conflicts with WLT Line 2 and BDark. The name of the line is SW Wild line at the moment.

After Navi communicates with BDark the plan is then modified. SW Plains, Birch Hill and Haruka Island are retained in the final plan, however due to another conflict be found by Isaaclao the line can no longer extend to Spawn, and terminates at the Yellowstone island Chong Shu Chau.

The route uses eleven 4-car SP1900 EMUs from WR's parent company, Suzuran Railways. These trains are from the 1900-1000 series. Each train features a unique colour scheme, and the driving cabs have been modified to allow passengers to look through the front of the train. The trains were manufactured by Kawasaki.

Four trailer cars have been modified by adding driving cabs, as no additional cab trailers were available in the Suzuran Railways fleet. These modified cars are identified with the suffix K.

Three formations (Z3, Z4, and Z5) also operate on the Kallos Express by QLR with prior approval from Navi.

Formation Z1 previously carried the Tears of the Kingdom special livery to celebrate Nintendo's announcement of The Legend of Zelda: Tears of the Kingdom. The livery was later removed following the MTR4 migration.

Beginning in May 2023, the trains received a texture quality upgrade originally created by Unknownkfa. However, following player complaints that the higher-resolution textures negatively affected gameplay performance, particularly on low-end PCs, the texture resolution was reduced to half of the original on 2 September 2023. Formations Z3 and Z10 did not receive the upgrade, and it was later announced that they would not receive it. Since the MTR4 migration, all trains have reverted to using the core mod model.

Plans were proposed during the early days of Let's Play to extend the route to Spawn. However, they were shelved, and Navi's statement on 1st August 2026: “Spawn area is too crammed, and the bus route still serves an important role in the Let's Play server, especially when no other routes serve the Icon Broadway. We have no intention to scrap the bus service, and extending the railway would further worsen the lag of the server in the Spawn Area.” further proves that Wilds Railway has no intention to extend the SW Plains line to Spawn.

Plans were discussed to allocate parliamentary services towards the Overground Chulainn Line to Cheung Ming.

All times listed here are in British Summer Time (BST).