Hong Kong has one of the world's most impressive skylines. The dense collection of skyscrapers, with the picturesque hills rising behind them, can be viewed from either the Hong Kong Island or Kowloon waterfront areas. The popular Peak Tram takes riders up to Hong Kong Island's super-touristy Victoria Peak (which has a viewing platform that sits on top of places like McDonald's and Bubba Gump Shrimp). A cheaper and more authentic alternative is to ride the iconic Star Ferry across the harbor. People actually still use these slow moving boats for commuting, but they are also great for sightseeing, allowing riders to see the skylines of both Kowloon and Hong Kong Island during the trip.
The ferries are crowded at rush hour, but the fares are very cheap, so you can easily ride several times in a single day. Longer rides to outlying Lamma and Lantau islands cost quite a bit more, but are still generally cheaper than a boat sightseeing tour (prices for these journeys range from $10-$20, depending on the route and speed of the ferry).