I know some people here who have a big running wheel for their Bengals which they love. Bengals are very athletic kitties so I wouldn't try to let them outside. If they want to dart they will be fast.
Plus while I agree that an outside life is great for kitties if there is no danger, the average life time of outdoor kitties here in Germany is 2 years
The lady who has the other apartment in our house (which consists of 2 apartments) has made the garden safe with a high fence for her three kitties.