Could not recommend Calais.

Were you thinking of travel by train then ferry? The foot passenger journey is possible - but the check in / transfer process is not simple. The ferry market is overwhelming focussed on the car / truck user and foot passengers get barely an afterthought.

If you wanted to visit the coast across the chennel, Boulogne and Wimmereux are far more interesting. However - they're harder (not impossible) to get to without a car at your disposal.