As a 35-year local, I can give a little insight into Columbus. It was a designed capital, so a major city with no metropolitan area. The downtown used to roll-up the sidewalks at 6 PM, but now there is some activity due to sports, the convention center, and even Pokemon-Go.
Must sees:
The Scioto Mile. A few years back they removed a dam south of Columbus and this produced a lot of prime land on the shores of the Scioto River. This is now a world-class park which is truly must-see. I don't think you can take it in with a quick stroll through it, but it is worth a look.
The Columbus Zoo is usually rated the number one zoo in the nation. Lately COTA (Columbus Bus) has teamed-up with them to give great deals if you take the bus to the zoo.
Jeni's Ice Cream. There is one just a block or so north of the convention center. It has often been listed as one of the best in the US. It has all those weird flavors. Pear Champagne is my favorite.
COSI - Center Of Science and Industry. There are no science geeks here, so never mind... It's across from the Scioto Mile.
For those who play Pokemon Go, I would recommend Goodale Park. a block west of the Convention Center. It should meet your needs. For those more adventurous, Schiller Park and the Franklin Park Observatory are also popular. If you are after rares, they seem to spawn a lot downtown at the Capital and at Bicentennial Park by the Scioto Mile.
Barley's Ale House #1 is across High St. from the Convention Center. Great beer, great food, usually an Origins mug (see coupon book).
This is not Indianapolis. Origins (as usual) coincides with Columbus Pride -- and the Convention Center is very close to the middle of it. Enjoy it, don't be afraid of it. You may see more than you want to see, but just say 'happy pride' and smile.
If looking for some good places to eat, Mac's is a Scottish bar just North of the Convention Center (other side of the street). Melt, a few blocks north is supposed to have some of the best fries in America. Valters in German Village has great 'authentic' German food from a great chef from Estonia. Near by that is Thurman's Cafe with hamburgers so big, one might be able to feed the country of Estonia (See Man Vs. Food), expect a wait.
Feel free to ask me about anything else Columbus-related.