Across Daxue Lu, south of Xiamen University, is this gigantic German artillery post built in 1894. You can rent binoculars to peer over the water to the Taiwanese-occupied island of Kinmen (金门, Jīnmén), formerly known as Quemoy and claimed by both mainland China and Taiwan.
To get here, walk for 2km south from Xiamen University along the coastal path or take bus 22 (¥1, 25 minutes, frequent) from southeast of the Zhongshan Lu walking street.