Tomatoes are mildly acidic, so something similar should get you an approximation of the flavor. Pickled onions might be a good choice, or some other lightly pickled fruit/veg (maybe beets for salad). Actual dill pickles are not going to be too acidic to be a good substitute (but are a great thing to put on sandwiches in addition to tomato anyway).

Pineapple might work in some cases, but it has a strong flavor and sweetness that won’t work everywhere a tomato does. Salsas are a good place for this as a tomato substitute (along with mango and corn), but pineapple does also work well in some sandwiches.

Genius. If you vaporize them they can’t melt.

I hear Greenland has WMDs - in the form of melting glaciers that will cause some kind of climate catastrophe. /s

I’ll bet you one upvote, and I’ll pay it right now!

Salzburg, Mariazell (specifically hiking through Ötschergräben), and anywhere in the Austrian Alps are all excellent.