On my visit drive along Highway 50 one of my "must visits" was Stokes Castle. This castle is on the outskirts of town behind the Chevron Station up an easy to navigate.
The Castle was built in the late 1800's, 1897 more specifically. It is definitely a unique structure that you cannot access but simply walk around. There is also an incredible view of the Austin valley from the hilltop.
Believe it or not, while I was there it was snowing. Not a lot, but it definitely was snowing. Austin sits at just under 7000 feet so just walking around will leave you a little winded.
Visiting Stokes Castle took about 15 - 20 minutes and is definitely worth a stop to complete your Highway 50 itinerary.