(Although I'm starting to worry that by posting so often about nature and ruins, I'm being misleading.)
This is Fort Serapong, one of 9 forts that the British used to unsuccessfully protect Singapore from Japanese occupation in WW2; built in the late 1800s.
It is largely off limits. This is due to the risk of concrete walls crushing you to death, which is unlucky.
However, there's still a washroom. Or maybe a kitchen.
The bolts that held the big warring guns in place are the longest lasting, to break your feet for decades.
Strangling fig: ambitious. Not intimidated by swallowing a whole building.
The inside view is fairly creepy.
Speaking of swallowing and creepy, here's a fun fact. This is the creeping cucumber, which is edible when green, but a strong laxative once black (background).