Fort Serapong was built by the British army in 1879, atop a hillock called Mount Serapong on Pulau Blakang Mati (now resort island of Sentosa).
It was modernised a few times, the last being in the 1930s. Serapong is a huge network of batteries, tunnels, underground rooms, lookout posts, supporting buildings and even its own water collection system. Essentially a self supporting defence post. During the WWII, Serapong saw little action. The role was to protect Singapore Port. Serapong was used to fire on ships in the harbour only a few times, before itself, along with other forts and batteries were shelled and damaged by the Japanese. When the British forces surrendered, all the batteries were abandoned. Some of the guns were destroyed by the British just before they withdrew. But what happened to the batteries during Japanese Occupation I believe isn't clear. The Japanese army capture many defence facilities for their own use. Like Fort Siloso was turned into a POW camp. As for Serapong I can't find any info online. What I believe was something gruesome might had happened inside the tunnels. As you know during the war, "comfort women" were set for the Japanese troops. I think the spirit might be some of them who didn't make it back.
Now Serapong is like a ruin, complete forgotten and overgrown by vegetation, save for some people who know of it's existance. Recently an archaelogical dig was conducted at the fort, which cut down vegetation growing on the fort and uncovered the gun mounts.
A few days ago me and a group of friends went to recce Fort Serapong, Sentosa at night, a personal outing.
At 11:30pm we reached the entrance of the tunnel and begun to sort our stuff. Then one of the participants heard someone talking outside, so we switched off all our lights (torches, latern, camera, videocam). What I thought I heard was a very faint "mmmm", "mmm" like people talking softly. All of us heard this. One person said he heard a tap sound, like tap on concrete. Then a strange thing happened during our "lights off" period. We were squatting down, except for one person who is standing up. And this person later said he saw another person standing and moving his head. We have no idea who this other person is.
We thought nothing much and proceeded in, tying a string to the outside to lead us in, in case we got lost. A lot of time was spent detangling the tangled spool of string. Midway, one person ( a lady ) said she heard 2 ladies voice speaking softly, like an exchange of dialogue. She heard it 3 times, once midway into the first tunnel, 2nd and 3rd time just before we descended down to the second tunnel, where there's a part of a c. 50cm drop. She said the voice was just beside her.
At the 2nd tunnel, I was holding to the cut end of the string tautly as one participant tried to detangle the spool. I felt the string vibrating, as if someone had rubbed past it. Thinking it might be my hand shaking (hands are never 100% stable), I moved the string up and down, but there's no vibration. Just might be my hands shaking, I'm not very sure.
We finally reached the end of the tunnel, where there's a verticle ladder down, estimated 20 ~ 30m deep. After some discussion we decided not to go down, as it was too risky. All the while I feel as if there were a lot of people in the tunnels, people everywhere. I was the only one taking photos, and numerous orbs appeared in some photos. Especially one which looks like a portrait of a young lady (orb showing head, hair and shoulders). The orb was captured near where the 2 ladies' voices were heard. Shocked The voices were only heard by the lady participant, btw.
We left the fort shortly after, at 1am.
This was posted by my fellow participant:
QUOTE
Hmm redstone i thought i got 2 people standing that is me and the other lady? and my biggest fear is ranger Cos when u guyz was untie the rope or something i heard people talking outside soo i thought it was the ranger petroling the place soo i was super scared of ranger and tell u guyz too turn off the lights" then when the lights are off i thought my frenz whose his name is weixue soo i thought infront of me is weixue soo his head was turning left and right quite fast as if he was checking the area soo below and say can open the lights liao then i say the weixue behind me soo i thought when i look below we go walk behind soo i didn't suspect anything weird till when we are at the 7/11 then they talk about when we turn our lights off and weixue say he was all the way behind me when the lights was off soo i was like ?????? but luckily when the lights was off i wanted to rest my hand at the guyz shoulder whom i suspected the guyz infront of me is weixue.. soo it must be my lucky day that i didn't rest my arm at the guyz infront of me.. 
What are your opinions of what we encountered?
Ah, sadly... no more investigations.