BJJ is a good cardio/strength fun activity that doesn't feel boring and is social.

Contact, and especially grappling type sports do tend to make people stronger since they involve a lot of grabbing, twisting, lifting, etc. of another person's body as they resist.

BJJ can be done in a playful and relaxed way or very competitive and grinding. One can do it a small space on cheap mats with friends or at a formal school or competition.

It's full of possibilities and things to learn so it doesn't get boring.