Whenever I hear the word "bore" I think of either a male pig (boar) or a person who drones on and on and on or to drill a hole. I had never heard of a tidal bore. Take a look at the Severn Bore. I think if I actually saw this I would be absolutely terrified. Waves in the ocean don't really phase me; I think they are beautiful. There's just something about this being a river that would scare the daylights out of me. Of course there are people who surf this-they call themselves boresurfers.
I would still love to see the Severn Bore even though it scares the living daylights out of me. Possibly viewed from a distance.
Another sometimes natural sometimes not phenomena are swales. A swale is defined as a wide depression in the ground or wide, shallow depression in the ground designed to channel drainage of rainwater or a wide flat roadside drain.
Some nice person has gathered some examples of swales.
Lastly, if you are in the mood for an optical illusion check out these beans/being.