The Achilles tendon part of the ankle, above the heel – seeing it bare, and especially seeing it bare above a bare foot and walking on hard pavement – I think that can be very strangely kind of sexy to me; it is so rare to see a clean and attractive heel.
I do not even like feet.
There is also that slender pair of what I assume are tendons that are just behind the knee, which disappears into the thigh, and is only really visible when someone sits with his knees up and his shorts sliding down his legs.
You have now idea how much porn and/or surgical imagery I encountered in trying to find, via Google, the correct terms for those damn tendons.