im planning a trip to japan. When should I visit? Spring or summer? What cities must I visit? List them. (for sure places like kyoto, toyko, osaka) what should I see in thoses cities? (like kaiyukan aquaium-osaka, nijo castle-kyoto, tsukiji fish market-tokyo.) Please name places or things like( sumop. Funky muesums or resturants. (like modern toliet). Name hotels and onsens. Famous things.
Depends on your interests, of course. What might interest one person might not another.
But if you want some ideas, start with http://www.jnto.go.jp
Spring is far better than summer, which is extremely muggy and humid in most of the country.
You don't have to limit yourself tightly either - get a JR Pass and go all over, or you can fly across
the country at huge discounts on an ANA or JAL Japan airpass.