Where would you go as a "back-up" vacation?

In late July I have training for work out in Las Vegas. The training is from Tuesday-Thursday, so I just requested off the Monday, Friday, and following Monday, and plan to make a short vacation out of the extra days in Vegas. My plane ticket is covered by work, and my hotel is covered for half the trip, and they’re going to give me the company rate for the remainder where I won’t be working. My girlfriend plans to fly out and meet me Thursday night so we can have like a long weekend in Vegas.

Well the trip may end up getting canceled if the company doing the training can’t get enough people to sign up for it. But the g/f and I will still have the week/weekend off. So we’re trying to brainstorm for “back-up” vacation ideas. One idea was going down to Mammoth cave and camping/hiking. Another idea was going over to Washington DC and site seeing.

We live in Columbus Ohio, and we’re limited on cash/time, so any idea would have to be within maybe half a days driving distance, or a flight to it would need to be attainable for low cost within days of the actual flight.

What ideas have you got for the “back-up?”