I’m Back! Blenheim Palace -> is well worth the third visit, both in terms of the site and convenience. A quick bus ride will take you from Oxford to the This is the family home of the Marlborough Family built as a thank you from the crown for the Dukes military victories (and the gratitude shows). It is also the birthplace of Winston Churchill.
I have visited Blenheim before, on my own and with my mom, but this is a site I truly do not mind visiting again and again (they also offer free year entry with admission ticket). This visit I focused on the house. The downside of long day visits is the mental fatigue so by the time I had finished visiting the house at Blenheim I just didn’t have the energy or desire to walk back out into the various walking paths in the grounds (although I have before and it really is worth it).