Refusing

I applied for a certain position at a company, but when they contacted me, the recruiter asked if it would be ok if I interviewed for a different position. I will give them the benefit of a doubt and assume the original position was either cancelled or filled and this was not the good old bait and switch. So after the phone interview, I became more convinced this position is not a good fit. Nevertheless, they called me in for an onsite, in a different city. I am inclined to refuse, as it would waste one whole day. However, I don't want to burn any bridges, as I expect to be applying in the future should another interesting position open up. How to handle this? P.S. I am currently employed.