Kowloon Park is a huge park in Tsim Sha Tsui since 1970s. It is in between Tsim Sha Tsui and Jordan Station, so you can go there from either station. It has facilities such as bird lake, pavilion etc. just like other botanic garden built by the British.
Above: top view of Kowloon Park from The One Mall
Take a look at the map. The north side (the side near Jordan Station) has multiple recreation facilities like Swimming Pool, indoor basketball courts etc, which visitors may not be interested in. Therefore you can visit from the South side, the side closer to Tsim Sha Tsui station.
The Chinese garden and different lakes are the most beautiful spots to visit because you will feel like you are in an oasis within the city.
Moreover, it will be the best if you are staying at an hotel in Tsim Sha Tsui. You can visit the park after having breakfast in the morning. There should be less people around and you can see local people practicing Tai Chi or Chinese kung fu. Another way to experience local life.