Anything spontaneous is nice, I promise. A walk after a movie is actually fine, honestly, but even something as simple as walking to an ice cream place! I love that.
Punch her in the jaw to show you've got good boxing skills. Then inform her of the dangers in ever letting her guard down. Punch her again in the gut to emphasize this.
It depends on where you live but a museum and art gallery binge is pretty fun. I live near Boise, Idaho and I mapped out all of the art galleries and museums that were open and visited them in one day. Me and my lady grabbed lunch halfway through the adventure at a hipster sandwich shop with homemade sodas.