What actually happens if you go
Nobody is expecting you and nothing is required of you. You can stand at the back and watch. You are not asked to say anything, join anything, or give a name, and you can leave whenever you like.
Dress modestly, in loose clothes that cover the legs; women also cover their arms and hair (many mosques keep spare scarves). Shoes come off before the carpet. Women’s and men’s prayer areas are usually separate and signposted. Friday around midday is the busiest time, so a weekday is quieter for a first visit.
If you want to talk to someone rather than just look, say so at the door and ask for whoever handles visitors. Most larger mosques have someone; smaller ones may not, and it is reasonable to ring first.
This is not a vetted list
These are map listings. This site has not visited, checked or endorsed any of them, and cannot tell you what any particular mosque teaches or how it will treat you.