Go big or go home. https://en.wikipedia.org/wiki/Chinese_treasure_ship

That small thing at the left is the Santa Maria, Columbus' flagship. The largest ships in the chinese fleet — called "baoshan," or "treasure ships" — were between 440 and 538 feet long by 210 feet wide. The 4-decked baoshan had an estimated displacement of 20-30,000 tons, roughly 1/3 to 1/2 the displacement of modern American aircraft carriers. Each had nine masts on its deck, rigged with square sails that could be adjusted in series to maximize efficiency in different wind conditions.

This thing screams shock and awe at full volume. It's gigantic, you have plenty of bouyancy to fill it with an entire army or all kind of equipment, you could throw a swimming pool at the center and the thing will not even notice. It's basically a floating city, just outfit it with good living space and supplies. However, those materials may work well in Pacific ocean. But give it a nice big freak wave and the thing is doomed. Stay in calm waters...

Something similar to your concept is a major plot point in Neal Stephenson's The Confusion, volume two of The Baroque Cycle. One part focuses on a few characters bartering for information about the route sailed by the Manila Galleon, a huge trade and treasure ship that was (allegedly) rebuilt every year because the ships were too large and unwieldily to survive more than one journey.

Stephenson also follows the journey and depicts some of the interactions between merchants whose wares are onboard the galleon. These merchants are shown as being largely unaware of the perils of the journey and unable to handle the crises that arise. They are shown to be one small but politically powerful contingent on the ship – due to their wealth – which was otherwise inhabited by Spanish military, sailors, soldiers, and some other wealthy travelers.

Whether the Manila Galleons were used in this manner or not, it was not uncommon for the wealthy and powerful to use mercantile or military vessels for their own transportation during the age of sail. Depending on the wealth, station and numbers of such travelers, such a sailing could become a de-facto pre-industrial cruise.

It is said that Cleopatra VI and Caesar took a cruise on the Nile and Caesarion was conceived during it. There is an elaborate description of the Thalamegos, a pleasure barge built by her ancestor Ptolemy IV (reigned 221-204 BC). Perhaps still in use in Cleopatra's time.

Alexandria and Alexandrianism

Thalamegos - Wikipedia

Thalamegos - Google Images

Thalamegos - German Language forum

Furthermore, the Syracusa, a super ship built by King Hieron of Syracuse, could not only carry vast cargoes of freight and not only had strong defenses, but also had elaborate passenger quarters.

Syracusia - Wikipedia

Athenaeus: The Deipnosophists

As we all know, emperor Caligula built huge barges on Lake Nemi, one a floating temple and one a floating palace. Suetonius also says:

He also built Liburnian galleys with ten banks of oars, with sterns set with gems, particoloured sails, huge spacious baths, colonnades, and banquet-halls, and even a great variety of vines and fruit trees; that on board of them he might recline at table from an early hour, and coast along the shores of Campania amid songs and choruses.

The Life of Caligula

So if Suetonius is correct Caligula also had seagoing yachts for sea cruises.

Caligula's Barges - Google Images

Emperor Yang of the Sui Dynasty (reigned 604-618) is said to have built vast dragon boats for pleasure travel on the Grand Canal.

Grand Dragon Boat in the Sui Dynasty

Emperor Sui Yang's Big Dragon Boat

But as a general rule people did not go on pleasure cruises until the mid 19th century.

As another entry in non-Ocean based "cruises", in the 1800's the Mississippi river was home to many paddle-wheel Steamboats, that became a means of entertainment in themselves, rather than just a means of transportation. Many were essentially floating saloons and gambling halls.

The steam power required to take them back upstream pretty much pegs them to the Industrial Age though. These are more of an example of why you generally needed industrial machinery to allow the size and free space to have a "cruise"-style vessel.

I think the closest you're going to get in the ancient period is a pleasure barge. These were used extensively on the Nile, and, as others have mentioned, rulers (or the truly obscenely wealthy) used similar constructions on inland lakes and rivers.

The problem, as others have mentioned, is that seafaring was still a pretty chancy endeavor. The closest you're going to get to ocean-going cruise ships where people had luxury accommodations and things to do are large boats used for state purposes (diplomatic visits by rulers, transporting an emperor to war). Even then, the only one who really had comfortable accomodations was the Big Important person.

• There were assorted royal barges.
• There are precendents for very large galleys.
• There were some cruises carrying pilgrims in the middle ages. The nature of the passengers might make this the closest to a cruise liner.

Until fairly recent years embarking on a ship travel was, to say it bluntly, gambling on your own survival.

This for a series of reasons:

• poor food
• lack of hygienic services and crowded environments
• lack of advanced sailing technologies (weather forecast, night or low-visibility navigation aid, radio communication)

While on a present day cruise ship a wealthy person can enjoy luxuries like a private Jacuzzi, cold champagne and a private suite, the best he could achieve on a pre-industrial ship would have been

• no bath for months
• dumping his own excrement off board "en plen air",
• a hammock in a crowded room
• water/alcohol mixture to ensure it was safe to drink

All these pleasantries for then reaching a place where most of the time hardly any civilization of European level was present.

To summarize, one would not start such a travel for the pure pleasure of the travel, but only if he had a real reason to do it (trade, emigration, religion, exploration).

The Nemi ships

Caligula built two barges on Lake Nemi, one of which was essentially a floating palace.

The key here is that the ships were on a lake, not on the ocean. Dying at sea is a lot harder when you aren't at sea. Smaller waves help with the seasickness situation. I would imagine that large, lazy rivers would be suitable for 'cruises' as well.