By day, the area behind Safra Tampines seems typical of a cluster of industrial buildings.
The eight blocks of flatted factories at Tampines Industrial Park A comprise car workshops, furniture makers and warehouses.
Come nightfall, however, the place transforms into a secret dormitory for foreign workers.
Some 1,000 foreign workers sleep in these workshops and flatted factories, hidden behind partitions.
At night, streams of lorries unload workers at these illegal dormitories.
Some of the dorms are in units marked "under renovation".
One person who tipped off The New Paper thinks there are about 8,000 people sleeping in these eight blocks at night.
TNP spent two weeks staking out the place. Going by the number of buses ferrying in workers, there seemed to be about 1,000 workers staying there.
The flatted factories are owned and managed by the Housing Board (HDB) and the illegal dorms are clearly violating HDB's rules.
TNP understands that most of the offending units are owned by companies that house their own workers, while some units are leased out to other companies.
The workers seem to be from a number of construction, electrical and manufacturing companies, going by the registration details of lorries ferrying them in and out of the area.
We spoke to the director of one construction company which has a warehouse there.
Twelve foreign workers live in the back of the warehouse. The unit also has a kitchen area and washing facilities hidden from plain view.
Said the director, who did not want to be named: "Here (in this area), there's a lot (of other dormitories), too.
"Just come down on their Sunday rest day and you can see for yourself."
He claimed the workers all have dormitories outside, but they told him they prefer to stay there.
When told that it was illegal, he said: "Yes, I know. You don't understand the construction culture here.
"The costs for hiring a foreign worker are getting higher and we're not a big company. If there are no complaints, then why not?"
During our stake-out, we saw workers in sarongs and pyjamas gathered at staircase landings and the roadside, where the Wi-Fi signal is strongest.
There is even a system to ensure the workers are fed. At around 7am, they collect food from marked boxes at the foot of the block, left there by caterers.
Before 9pm, when they return from work, they collect dinner from these boxes.