Sometimes you just want to get away from the kids. Here are some things that adults can enjoy without little ones around.
Casino
While out at sea, the casino opens and those under 18 are prohibited from being in the casino. Yes, sometimes you'll see families or teens cut through the casino, but they aren't there for the most part. Gamble away!
Both the spa and fitness area posts notices that guests must be 16 years+ to enter or use these areas. Take advantage of the peaceful spa massages, facials, or sauna/steam room. Not only are these activities relaxing but healthy for you too. Whether working out alone or with a travel companion, you will enjoy the tranquil view of the ocean while you work out. Occasionally there are a variety of classes you can attend as well.
Bars/Lounges/Dance Clubs
Bars and lounge areas totally frown upon under-age cruises entering. Adults that travel with kids usually don't bring them in, but I will say that I have seen it. The one area that enforces age of attendees is the dance clubs. In fact, earlier hours of the day are specifically for those under 18 years. After a certain hour, only 18+ allowed. Piano bars would be the most likely alcohol-serving area that you might see kids, but usually adults know better.
Late Night Comedy
Comedy shows at 11 pm or later are specifically designed to be R or X-rated and are no place for kids. The crew make several announcements and postings that material/content is not for those under 18 years. Besides, most kids should be in their cabins by this hour.
Outdoor Serenity Lounge Area
Many cruisers are not aware that most ships have a special, secluded area of the ship (usually at the very back of the ship or a small, upper area in the center of the ship) that is meant exclusively for adults. It is usually an area that is a little difficult to find and out of the way. It may even be an area where bare top sunbathing is allowed. If you cannot find this area, just ask a crew member.
Art Auction
Rum Party Boat Excursion
Caribbean, Bahama, and Jamaican cruise itineraries usually offer at least one rum party boat excursion. Some are daytime yet others are sunset 2-hour mini-cruises that serve all you can drink rum punch. You can always spot the cruisers that are just returning from one of these excursions. The wobbling and weaving give them away. Need I say more...
If all else fails, you can always hid in your cabin and create your own activities....