Exercise forms that don't place stress on knees or hips?

I'm currently going to physical therapy and am unable to do the majority of my workout due to it causing issues with my hips and knees. What are forms of exercise (especially cardio) that wouldn't put stress on these areas? I've thought about swimming but that turned out not to be a possibility. Thanks :)
Exercise forms that don't place stress on knees or hips?
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