Yeah, I know how it is. I once had such a trip. 18 days through Italy, France, Spain and Austria. You see lots of things but by the end of the 5th day you don't feel your legs at all and around the 8th day you fall asleep in the bus at 8 pm, just to wake up at 8 am, 600 km away from the place where you fell asleep.
For the guide it's much worse.
But God it was worthy.