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!
Please note new GZ coordinates at N1 21.1668, E103 51.4691
(Apr 2016) This cache has been updated to make it easier and with previous waypoints removed. Previously, the GZ was in an underground sewage tunnel that required climbing and crawling. 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.