Recommendation for countries and places/sites that are a must visit in Schengen Area countries. I have 8 weeks and my primary landing destination would be in germany, in Dussoldorf.

I will be traveling with friends and would like to know any books to buy or areas in schengen area please that people have being too that are highly recommended. I am into museums and popular tourist sites like the tour eiffel. Also any caveats, tips, tricks you have discovered along the way.Any decent hostels and hotels you recommend that were affordable. 40 dollars a night would be my price range of affordable for a hotel.