This house in Japan includes quite an aspirational example of an indoor rock garden, but that's sometimes the best inspiration, isn't it?
Designed by Suppose Design Office, the house is situated on a small lot that doesn't include much outdoor space. Instead, the client wished to have an indoor room dedicated to a "garden".
The same could be done in a small apartment, albeit on a more modest scale. Imagine tending a small rock garden in aquarium, a handmade wooden tray, or out on the balcony - even in a nonworking fireplace!
Images: Suppose Design Office