Here is some information about some cycle routes on the southern edge of Haikou city.
The map below shows the Longhua District cycling area (the red square) in relation to Haikou city. The cycling area is south of Haikou city, inbetween the central highway and the eastern expressway. Paths suitable for cycling begin on the southern side of Yehai Avenue (椰海大道), which is basically the edge of the built up city.
The Longhua area is an old volcanic area (there are no active volcanoes). The area has abundant amounts of volcanic rock just beneath the top-soil. As a result, you can find many rock cutting factories, quarries, and some small ancient lava rock villages. The roads are generally small concrete or tarmac affairs interconnecting the small farming villages. Most of the area is tropical countryside. Traffic is sparse apart from around the new Mission Hills Golf Resort where there is construction and big trucks moving lava rock. The altitude is roughly sea level and largely flat.