4 Days in Iceland's Golden Circle

I did Iceland last fall, solo, as a 6 day whirlwind tour around the loop road (yes, it was awesome). This fall (late Oct) I’m getting 4 days with the wife and am looking for the coolest excursions around the Golden Circle, which I mostly skipped last year. We’ll be staying south of the GC in Selfoss with a small 4WD vehicle,...