Ah, those great vacations, those romps through cities and lazy days on the beach, those warm evening theme-park fantasies.

And every one of these will include a nature hike. Even in the middle of Paris or Rome or New York. Because here's a hard-and-fast rule of family vacations:

When nature calls, you take a hike.

Nobody talks much about these sorts of nature hikes — they're so much a part of being alive, you just take the hike without comment. When you're on the go and you gotta go, well, you just go a little more quickly — it's really a basic element of travel. I wouldn't exactly call it adventure travel, but it could be an adventure, for sure.

No less a seasoned traveler than Arthur Frommer steps in to address this aspect of traveling, bringing it into — I apologize in advance — full relief. The great guidebook writer has authored a free 76-page booklet called "Where to Stop & Where to Go." It came out sometime during last summer's vacation season, but I didn't pay it much mind. At the time, I was preoccupied trying to find a restroom in Singapore.

It's one thing on a family vacation, when the kids need to go and you're feeling helpless to resolve the situation, while time — a deadline that can come any second — is of the essence. You're often initially helpless, and when the crisis is resolved, you feel like a superhero. (If only to yourself. Kids have a way of simply expecting super-heroism without fail.)

It's quite another thing to be traveling on your own and actually suffer the urgency yourself. Many of us are adults on diuretics or other meds that make us feel like thimble-bladders. I am among you, and I'm also an ardent traveler. And I understand how people may chuckle at the situation, which means only that they are not in it.

Frommer didn't write "Where to Stop & Where to Go" specifically for family travelers, although the book is perfect for anyone traveling to one of 19 urban hot spots in the United States, or to our four most popular national parks: Yosemite, Grand Canyon, Yellowstone, and Great Smoky Mountains.

He partnered with the pharmaceutical company Novartis, which published the booklet and will send it to you without charge. Novartis makes one of several medicines used in the treatment of overactive bladder — a condition affecting 33 million Americans.

"As a nation, we lag far behind other wealthy countries in creating public restroom facilities," Frommer writes. "The number of U.S. cities with non-beachfront restroom kiosks on their streets can be counted on less than the fingers of two hands; it's as if the need to go to the bathroom does not exist."

He says travelers with overactive bladders "have been inexcusably neglected by travel journalism." I would expand that to travelers in general.

"What a treasure of awesome sights and attractions our country has!" Frommer writes.

He is not referring to restrooms. Frommer skillfully ties the attractions of a place to basic bathroom information, and once I began looking through "Where to Stop & Where to Go," a question struck me: "Why haven't guidebooks done this all along?

Frommer says that "bodily functions are not usually a topic of polite conversation." Once he overcame his timidity about posing restroom questions to city officials, hoteliers and the like, "it was replaced by a sense of dismay over the failure of many U.S. cities to do enough to enable their residents or visitors to conveniently perform these basic human functions," he says.

For most readers of just about anything, the mark of a good piece is this: Does the writer cover things I know with the same wisdom as my own? Being a typical reader, I immediately flipped to the Philadelphia chapter.

In three pages, Frommer flushes out the high points: history, art, the city's streets — even the tourist-shuttling Phlash. And the city's prominent commodes.

Philadelphia has no official policy for providing public restrooms, he tells us. That doesn't mean they're not there. The Art Museum: "To get to the restrooms without paying an entrance fee, step around to the back entrance. They are down the hallway on the left." The Free Library, overlooking Logan Square: "Cross its massive lobby and descend 29 well-worn steps." The Franklin Institute: "Outside the ticket gates, a few steps behind a mammoth, seated statue of Franklin."

He covers where to go — and I mean that in its widest usage — at Reading Terminal, the Rittenhouse Square area, and, of course, our downtown national park.

The one major Center City attraction without convenient restrooms: "Busy South Street, which is lined with offbeat cafes, boutiques and pubs. In a pinch, use the facilities at one of the coffeehouses or bars, or ask a shopkeeper to direct you to a nearby establishment that makes restrooms available to customers — and visitors. It works."

Frommer offers some general tips: