Shitogo Gajumaru-en Banyan Garden is a useful open-air break in the Yakushima itinerary. It is less about ticking off a monument and more about slowing down: walking paths, greenery, viewpoints, water, or seasonal colour depending on the site. It is a little away from the tight centre, but still close enough to fold into a half-day plan if the subject interests you.
Bring sensible shoes and a little time. Places like this are often best in the morning or late afternoon, when the light is kinder and local walkers are out. If weather has been poor, expect muddy paths or reduced visibility, and check access before making a special journey.