Hong Kong is part of China but has its own visa rules and its own currency and is often listed as a country; for these reasons I am listing it as its own country.
While Hong Kong is well known as an economic powerhouse with a skyline dominated by modern skyscrapers it is includes a number of green patches and hiking trails that are impressive.
Statue with Hong Kong skyline in the background. Taken near the art museum in Kowloon.
The modern city is easy to get around with a great subway. The subway uses the Octopus card which is very convenient. The card can be used in many stores just by tapping it near the register (and can be topped up at many stores). The express train to the city also takes the card. I recommend getting the Octopus card, it makes paying very easy.
You can get by with English without any problem (signs include English all over, including the subway).
Getting a sim card for your smart phone or tablet is simple and provides a great signal (much better than my internet connection in my home in Malaysia).
I bought a iPad mini before my trip (which also included Guilin, Yunan and Shanghai in China) to help as I traveled during the day. I also created special maps linked to information on the sites to make it easy to find nearby attractions while I traveled around on my iPad mini (using the GPS and mapping). Here is my, Curious Cat Hong Kong Tourist map which you may find useful.