Fergus,
Assuming you have seen the job before quoting, there are many windows (next to the river, I think) that cannot be accessed using wfp, I am also sure you will need scaffolding (spelling) and I am not sure how many people you have but I'm quite sure it took a team a week just to clean the windows - not a builders clean. As for a water supply, I'm sure they have a tap there. Good luck getting recruits from your trip to Poland!
Other than that its a pretty location, and plenty of sites to see, I would recommend having lunch on a river boat!
Mac