Regarding the Cabinet (Churchill) War Rooms, my travel companion (though not wife, then or later) went through four stages when I told her I wanted to visit those:

1. The day before: "Have fun, dear."

2. The morning of: "I might as well go along."

3. After chatting with the couple at the next table at lunch, who had just visited them: "They might actually be interesting."

4. After our visit: "I had no idea they would be so fascinating!"

In case you're wondering, I recommend them highly. Might not fit everyone's definition of "off the beaten path," they're not exactly a secret, but well worth the time.