"Cross Frog" is a well-established route in Hong Kong. If you look at Hong Kong Island on the map, its shape resembles a frog. If one hikes from its eastmost point to westmost point, the GPS track appears as a line that crosses the frog. The route has a variety of conditions, including:

- Steep climb, e.g. 250m ascent in 1KM distance in Old Peak Trail

- Long paved/ highly runnable segments, e.g. from Tai Tam Gap to Tai Tam Upper Reservoir which is around 3km in distance with 100m decline

- Stairs up/ down in some places

Start at the metal gates leading down to the footbridge across Yongding River, just west of Anjia Zhuang 安家庄 on the G109 road. End at the engraved stone at the entrance to Baihua Shan Scenic Area 百花山自然风景区. Don't forget to reach the highest point at c. 2020m (百花山主峰), which marks the end of the ridge line, before turning back about 2km and heading down the main path to the entrance of the Scenic Area.