I have a 5 hours transit today at Hong Kong Airport, and so I decided to visit Kowloon/Mongkok. However, I also want to enjoy Hong Kong Station. I don't have HKD in hand so I cannot take a train between the two station, although I can take Airport Express which can be purchasable via credit card.
In this case, can you still enjoy both places by walking across, possibly via a submarine tunnel, which I think a bus/train uses?