@dadpad,
Spend a few good days in London where they have some of the best museums in the world, and most are free. It's also easy to move around in London by Underground, and a day pass or a three day pass will be worth the price. You don't have to eat at expensive places, and chow down at some pub for home-cooked meals at reasonable prices.
Also, I'd take up Walter on his offer; he's a very good host, and will show you around places most tourist do not go. Just hang onto your hat when he drives on the autobahn; he has a lead foot.
Europe is great, because you can travel to so many countries with easy access by plane or train. You can also play it ear, and plan as you travel from one place to the next like I did many decades ago when I did a Eurailpass for two weeks and visited about seven countries.
Good luck on your plans.