Alam8 The Swiss Travel Pass would be a complete overkill for what you seem to intend, as it’s valid in entire(!) Switzerland. So what restrictions exactly are you referring to in this particular context?
In other words, getting a 3 day STP just for sightseeing in/around Zurich would be like paying for a full buffet breakfast in advance and just grabbing a glass of water and an apple…
You might rather want to look into this option It has a smaller area of validity (check the map), but includes some museums and other goodies.
Or maybe this option This one has a larger area of validity (= entire Canton/State of Zurich), but covers transportation only. As opposed to the Zurich Card, this would also include the long boat cruise on Lake Zurich up to Rapperswil and back, or even getting to Schloss Laufen (Rhine Falls) via Winterthur. (Warning, not further than Schloss Laufen, as crossing the Rhine = state border by train would require an additional extension ticket. But that railway bridge over the Rhine above the falls has a pedestrian footpath, used by most visitors)