It has been the ruin of many a pleasant outing: nature calls, but there's nowhere to go.
Now, a new website is making it easier for tourists to get much needed relief when travelling in an unfamiliar city or town.
The site, Airpnp, is modelled after the popular lodging website Airbnb, in which homeowners make their spare rooms or unoccupied dwellings available to paying lodgers for a fee - often considerably less than the cost of a hotel stay.
In a similar vein, users of Airpnp are matched with bars, restaurants, offices and homes where they can pay to use the toilets, albeit for a fee of US$5 or less.
The idea was the brainchild of Max Gaudin and Travis Laurendine, two New Orleans natives - they call themselves "entrepeeneurs" - who have encountered the problem frequently over the years during that city's riotous Mardi Gras festivities.
Fat Tuesday celebrations in the southern US city, held this week, are marked by an abundance of drinking but too few places to discreetly and legally relieve oneself. The toilet shortage prompts some to resort to public urination - a criminal offence.
Airpnp solves that problem by connecting people willing to share the toilets in their private bathrooms with strangers willing to pay for the privilege.
"When there aren't enough bathrooms nearby for the amount of people in any given location, Airpnp is there to save the day," its website said.
Users can select from among pictures posted on the site, which also have descriptions of the amenities. In addition to the site's dozens of toilets in the United States, there are also about 120 bathrooms posted in Europe on Airpnp.
The site's founders say a smartphone app is in the works.