Almost all cruise liners dock in Stazione Marittima. Some cruise lines provide transport from there to Piazzale Roma where water buses or private taxis will carry visitors all over Venice, or land transport can carry them to the mainland. Otherwise land taxis can be hired to drive as far as Piazzale Roma, which is as far a wheeled traffic can go into Venice. If luggage is light then it is a walk of 500+ yards from Stazione Marittima to Piazzale Roma.There is also a People Mover monorail from Piazzale Roma to the dock gate and Tronchetto that can be useful if your ship is moored near the dock gates.