Best items to use on years of caked on soap scum in a shower?

Take a damp sponge and pour a generous layer of baking soda --scrub a bit with sponge (or a stiff brush & don't forget to close the drain!) and then pour some vinegar over it and watch it bubble. I would even let it sit overnight. -- You should see a difference.

Mix baking soda and vinegar so that it is a paste then use it to scrub the walls and doors. Works great!

Water and white vinegar 50/50 a dash of soap and a dash of jet dry.Use this with a Mr.Clean Magic eraser.Then once clean wipe it down with a used dryer cloth to eliminate streaks.

I used a credit card to clean one. Scraped it off well. Then used the cleaners to finish up.

I just recently used a steamer. Made the shower look brand new. Be patient though...it takes a bit of time.

Scrape off the bulk of the buildup with a razor blade. Then mix vinegar and Dawn half and half. Spray on generously. Let it sit for a while. Scrub. Repeat if necessary. Use the vinegar/Dawn mixture often to prevent any further build up. It works on showers, sinks, toilets, counter tops (not marble)...even tile floors. My miracle cleaner!