<<"Access to the park from the Seilbahn is on level ground, and there is a nice view over Zürich, the Zürichsee (Lake Zürich) and the mountains beyond.">>
Great idea - glad that you have a good memory of the area.
Here is an aerial image from SwissTopo
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I did not recommend it because I could not remember the region around the Bergstation. Every time I have gone up there, I have been meeting friends, and I (and we) have always immediately looked up the hill, since we we immediately started the walk uphill - either toward the forest or to the restaurant, and I have only come down at night, usually rushing because a car was about to leave.
It should be the perfect answer for Sulnata. Of course, a clear day is required. ;-)
If they want a nice walk, they could walk over toward the Zoo or the last stop of the #6. However, it may be more than the older members of their party would want to do. For some reason, I have always come down on the #6 in the daylight.
I found a photo taken in early November 2014 from near the Zoo. As noted before, at that location you are too far back from the "edge" to see the city itself.
However, it is a nice view of the clouds over the mountains, even if a bit hazy.
There are some beautiful places on the lake itself. I have attached some photos taken near Hurden and Rapperswil, several miles further along the lake to the southeast, at the place where the road and railroad cross the lake at a shallow spot between Pfäffikon and Rapperswil. It takes about 45 minutes to get there from Zürich main station. The walk across the narrow place in the lake is easy, with a nice boardwalk through the nature preserve.
But, it is a bit far from Zürich for a casual visit.