A note to be taken, try limit your sub-folders to no more than three level deep, a deeper page simply means that the page is less important and may get less attention from search engines as well as harder for readers to reach the page. For example :-
domain.tld/one/two/three/page
Ideally, two level is good enough for small to medium websites, for websites that has a larger list of categories, there may be a need to have one extra level to contain sub categorise instead of overflowing the main menu. For example, a website with large collection of recipes :-
Main menu
Recipes
Fruits
Meat
Seafood
Noodles
Salads
Sub category for Meat
Chicken
Pork
Beef
Sub sub category for chicken
fried chicken
BBQ chicken
sweet and sour chicken
Just remember the objective is to group web pages of similar topic into categories but be careful not to over categorise, a website with too many sections can be a bad navigational structure if each section contains only a few web pages in it. There is a golden rule to follow :-
Maximum three clicks to reach the desired page
Back : Categorise your web pages
Next : Link to industry leader related to your web page theme
