In the foothills above the plains of Tainan, Guanzihling is divided into two parts: "old" Guanzihling in the valley near the hot spring source, and the "summit" (山頂) atop the nearby hill. As the names hint, the old part has older, cheaper hot spring resorts, while the hilltop has newer, pricier ones.
Even by Taiwanese standards the romanization of the name is confused: alternative spellings include Guanziling, Kuantzuling and Kuantzeling, and until recently written the Chinese characters were written as "關仔嶺".
Buses leave hourly on the hour from Chiayi's Zhongshan Rd bus station, several hundred meters down the street from the TRA railway station. The journey on rattletrap local buses goes through Baihe and takes around one hour ($79), crossing through old Guanzihling and terminating at the summit near the Toong Mao resort. Alternatively, you could take a taxi, which will cover the distance in around half the time for around $400.
There are also eight buses daily (30 min) from TRA Sinying (新營) station.
Sightseeing in Guanzihling requires your own wheels, but traveling between the two parts on foot is reasonable. There are three possible routes: the meandering main road (~2 km), a fearsome pedestrian staircase (好漢坡) of about 300 steps, and a wooden stairway that passes by the hot spring source (温泉源頭).
Guanzihling is famous for its muddy hot springs. This may not sound very appealing, but the waters have a reputation for treating skin allergies, and the spring is reportedly one of only three of its type in the world (the other two being in Kagoshima, Japan and Vulcano, Italy). The standard course of treatment is to slather on the stuff, let in dry out for a few minutes, then rinse it off in a pool and repeat.
Dry hot spring mud for your own treatments is sold in every souvenir shop in town (around $50 for a half-kilo bucket).