Octopus is a type of currency/card for Hong Kong transit that allows you on *most* but not all ferries, subways, and I think all busses and most trains. We did not use it but I sure liked the sign – this was at the Ferry Pier to Lantau Island.
Ferries are one of the coolest things about Hong Kong. There are dozens of piers along the main waterfront heading off in all directions – to Kowloon, Macau, Lantau, and many more places. Be sure to take at least one trip on the Star Ferry from Hong Kong to Kowloon, and try to return about 8pm when the waterfront of Hong Kong is lit to showcase the many tall buildings and skyline. There are also tour boats for this sight.
Unfortunately for us the mist and fog was so thick in both Hong Kong and Shanghai that we missed most of the glory of these bright waterfront cityscapes – two of the most stunning in the world.