The tunnel is a single loop, and in the dark, you can't tell its shape or size.

隧道是一个单环在黑暗中，无法分辨它的形状和大小。

In its long history, it has never been expanded, remaining as a single loop line with a mere 15 stations.

在其漫长的历史中，它从未被扩建过，只是一条只有 15 个车站的单向环线。

The tunnel is a single loop, and in the dark you can’t tell its shape or size.

隧道是一个单环， 在黑暗中你无法分辨它的形状或大小。