Yes, you are absolutely allowed to get off a cruise ship at most ports of call without booking an official "shore excursion." This is often called "going independent." When the ship is cleared by local customs, you simply walk down the gangway and explore the destination on your own. You can walk into town, take a local taxi to a beach, or use public transport to visit local landmarks. This is a great way to save money and avoid the "bus tour" crowds. However, there are two major responsibilities: first, you must ensure you have the correct visa or entry requirements for that country; second, and most importantly, you must be back on the ship by the "All Aboard" time. Unlike official excursions, if you are delayed by a local taxi or a late train while exploring independently, the ship will not wait for you, and you will be responsible for the cost of flying to the next port to rejoin the cruise. For this reason, many independent travelers plan to return to the pier at least two hours before the scheduled departure.