Favorite thing: Within the Yarkon Park is the Seven Mills historical site. It consists of a series of milling stations along the river. Today there is little left or preserved, but if you follow the map to the various stations along the river it is a very plesant walk. Here you can see the signpost (sorry it is only in Hebrew here) and the map that accompanies it.
Favorite thing: Not that we're lacking nature in Tel Aviv, but the city grows rapidly and many green spots are being hidden behind the skyscrapers. Yarkon Park is found in Tel Aviv and running along its border with Ramat Gan. This park offers may different activities. You can walk (and it is a long distance), you can bike or rollerblade, lay on the grass, have BBQ party, or rent a little boat and to "sail" it in the Yarkon river, after which the park was named. Can't count how many times I've been there, I simply love this place.