On a tour of London's public loos, you have the opportunity to sample the sights, sounds and smells of the capital's toilets.
It might seem a peculiar pastime, but our guide Amber assures us it's popular with Brits and tourists alike.
We come to a stop on a bridge crossing the River Thames. "London's first toilet," we're told, before Ancient Rome brought sanitation.
Since then, public loos have moved on somewhat, but now they're in danger of going the way of the Romans too...
In the past decade, 40% of public toilets across the country have closed, according to figures from the British Toilet Association.
Six hundred are believed to have shut in the last 18 months alone, with 22 more under threat.
In north London, the Pond Square toilets face closure, because of cuts to local government funding.
The council explains that it has to make "huge savings" across its services. It is now working with local groups to try to keep the toilets open.
But campaigner Allan Rapley warns any closure will affect more than just the local community.
"Everybody needs a toilet, but some people need it more than others," he says.
"I suspect this toilet is used more by visitors than residents... lots of people are aware of its presence and rely on it as part of their working day like van drivers, taxi drivers, and delivery people."
Many public toilets have been sold off and converted into underground cafes, bars and restaurants.
One former lavatory in east London sold for more than £1m last year.
For historian Lee Jackson, author of Dirty Old London, at least it means historically significant buildings don't fall into disrepair.
"It's nice to see that they're being brought into some sort of use rather than being completely abandoned," he says.
"But I do wonder if councils have actually looked at the needs of the public... the rate payers of London paid for these spaces and now they're being sold off at a vast profit."
And with every closure, Gillian Kemp believes we're heading towards a new public health problem.
As leader of the Public Toilets UK campaign, she's calling for loos to be protected by law.
"It affects women, especially if they're pregnant, it affects children, older people, people with medical conditions, the list is endless.
"The ideal would be to have public toilets as a statutory requirement."
Alternatives are emerging in the face of closures - 'pop-up' urinals - which are far cheaper to maintain.
The Community Toilet Scheme, too, has grown in recent years - where businesses sign up, welcoming the public to use the premises when in need of a quick pee.
This, undoubtedly, will help to fill their tills too.
If the public loo does continue its disappearance, we may be spending more actual pennies in our search for the toilet, along with the metaphorical ones.