How to get there -
Take MRT to Tanah Merah Interchange. Then, take bus service number 2 all the way to the Changi Village Terminal. After that, head towards the direction of the Changi Village Hotel. You should walk pass it, on the footpath. Soon, you will be able to see a chalet, and beside it is a hill. OCH is the building on top of the hill. There is a long staircase, so there is no need to trek up.
Oh ya, there was a lot a lot of cats and kittens at the chalet beside OCH :) . One of them was actually so friendly that it followed us to OCH. At the stairs, when we went up towards OCH, the cat continuously kept "meow-ing", and it seemed like it was warning us not to go OCH. But, in the end, it came up and went into OCH. But when we came out, the cat was gone.

Also, we met 2 groups of people. One of them was a 3-person group and was holding fishing poles. Another was a group of Indians (no racist ideas intended), who asked us for spray paints and markers.
Inside OCH -
There were a lot of leaves, glass shards, debris and vandalism. It was old and run-down, giving creeps to those who went in. Enough saying, let the pictures do the talking :) .

The stairs leading to the entrance of OCH