Guanhao is an island in  Paradise where the World Government organized a training camp for future Cipher Pol agents.
The island is covered by a forest. The only known building on the island is a high tower with trees on a roof.
See also the associated category: Guanhao Residents.
World Government uses Guanhao as a training camp for future Cipher Pol generations. Rob Lucci and other CP9 members had trained on the island until they became strong enough to become full-fledged agents.
Lucci and other CP9 members returned to Guanhao after recovering in
St. Poplar.  Very Good pursued them but he was easily defeated. 
The tower on Guanhao bears a resemblance to the East Tower on Jiang Xin Yu in
Wenzhou.  The island may be named after a Chinese fan who asked Oda about the tower mentioned above. The fan's name is Wu Guanhao (吳冠昊).