Singapore is a country in Asia.
Hitchhiking
Hitchhiking is very rare in Singapore, mainly because it is a city and public transport is very common.
For those who are crossing borders to Malaysia, there is a Woodlands checkpoint in the North and another Tuas checkpoint in the West.
By boat
There is one ferry to an indonesian island. Forget about entering the singaporean port, I think the only way are the marinas. Get a yacht. There is one marina that lets you also enter without being member right next to tuas checkpoint.