There are many underpasses under the CTE, but this one is not well travelled and not many know it exists. It hosts an "art gallery" and resident bats. At my last visit, the walls had been painted over to make way for a new and upcoming exhibition. Do post photos of your favourite pieces as they come up over time!
This cache was created after archiving (GC12ZZ2) which was a multicache, and to make it easier. This is now a level 2 cache and accessible to most. Do be careful at GZ though, and to not fall into the drain!
You may start at the listed coordinates, or approach from Mei Hwan Dr or the Bishan Depot.
For those who don't mind climbing and crawling in a sewer tunnel, the original GZ is nearby and now re-published as GC6FAX9. Be warned that it is a T3 and not for everyone though.