The boundary between Hong Kong Special Administrative Region and China can be regarded as the "frontier of Hong Kong", because there is immigration control or "closed" except to residents on the margin of the border. The Hong Kong side  is patrolled and controlled by the Hong Kong Police Force to prevent "illegal immigrants" crossing from Hong Kong to China and vice versa.  As China's economic development catches up with Hong Kong, some parts of the border are no longer "closed", hence it is possible to run along the border area.   This is exciting because it is "new".

The Midhurst Way is a long-distance route from Haslemere to Arundel, West Sussex, passing through Midhurst and covering approximately 29 miles from the start point at Haslemere Station to the finish at Arundel Station. It visits Camelsdale, Kingsley Green, Fenhurst, Henley, Easebourne, Midhurst, Lodsworth, Tillington, Coultershaw Bridge, Chingford Pond, Bignor, Westburton Hill, Houghton Forest and Fairmile Bottom in the South Downs area of West Sussex.
 

Tour du Carlit dans les Pyrénées Orientales à partir de Porté-Puymorens

The Mendip Ring is a long distance path in 9 legs using public footpaths and other rights of way to follow as closely as possible the boundary of the Somerset (UK) local government district of Mendip.

http://mendipring.org.uk/