I think in terms of skill level, few things come anywhere near Windsurfing.
Hand on heart the longest learning curve and most rewarding sport once you can finally do it.
And the first time you get in the harness and start to plane is a feeling to behold, the first time you do that and get in the footstraps is better than any chemical high!
Haven't windsurfed for about 8 years now, Vasiliki in May – hope it's like riding a bike… 🙂