Sengan-en — sometimes called Iso-teien — was built in 1658 as a seaside retreat for the Shimazu daimyo and remained their main residence after they lost their castle in the Meiji period. The 50,000-square-metre stroll garden uses the bay as its pond and Sakurajima as its mountain, an idea so audacious that no other garden in Japan has copied it convincingly. Bamboo groves, a waterfall, a small bamboo grove and a Chinese-style stone gate fill the landscape in close quarters.
The Shoko Shuseikan museum behind the garden is a separate ticket but worth it: this is the surviving stone reverberatory furnace and machine works that the Shimazu built in the 1850s to produce iron cannon, glass and cotton — the first Western-style industrial complex in Japan, and now part of the UNESCO Sites of Japan's Meiji Industrial Revolution listing. The complex is about twenty minutes by city-loop bus from Tenmonkan; the closer Sengan-en JR station now stops here as well.