The Sentō Gosho is the second imperial property located within the Kyoto Imperial Palace Park (the other one is the Imperial Palace itself). The structures are not particularly grand, but the gardens, laid out in 1630 by renowned landscape designer Enshū Kobori, are excellent. Admission is by one-hour tour only (in Japanese; English audio guides are free). You must be over 18 years old and bring your passport. Your ticket can be printed or shown on a smartphone.
The palace was originally constructed in 1630 during the reign of Emperor Go-Mizunō as a residence for retired emperors. It was repeatedly destroyed by fire and reconstructed; and continued to serve its purpose until a final blaze in 1854, after which it was never rebuilt. Today only two original structures, the Seika-tei and Yūshin-tei teahouses, remain.
You can book tickets in advance at the Imperial Household Agency office or online. Same-day tickets (for afternoon tours only) go on sale at the palace from 11am and are on a first-come, first-served basis until capacity is sold.