Shitennō-ji (四天王寺) in south Osaka is one of Japan's oldest Buddhist temples. It was founded in 593 by Prince Shōtoku, an intellectual and devout Buddhist of the Asuka period who worked to promote the religion more widely throughout Japan. Rebuilt over the years, the oldest part of the site is a stone torii (Shintō shrine gate) dating back to 1294. While you can freely explore most of the temple grounds, admission is required to enter the main hall and climb the five-story pagoda. Honbō-teien strolling garden here is also worth a look.
On the 21st of each month, a flea market sets up outside the temple, selling antiques and knick-knacks including porcelain and old kimonos.