I didn't know why it was tower either. Had a look at answer sites and none the wiser.
20D word for type of "grub" that you cook
22d Princess Marina....there is a Kinks song about her.....she had a hat apparently, and marina- a small harbour.
The one that really got my goat is "American's right where the queen's portrait is" 2,3,5
(is it an American expression? The clue works better without it!)