D&D is an RPG, a role playing game. Characters play a role in a story.
As a DM, you're writing everything except their characters. So, if you want them to have the opportunity to interact with things you've put into the town, you need to introduce it to them in an interesting way.
You said you put a carnival with games and prizes into a game and they never explored it. How did you lure them to it? Did you just tell them it was there? Or did you drop some hints that there was something there worth seeing?
"As you walk down the road, Argath (he of the high passive perception) spots a young man following the party. He is a good distance back from you but is clearly watching the group and following after them. however, just as you realize this, the young man turns down an alley that leads to the edge of town, where the carnival is set up."
"As you relax in the tavern and discuss your recent adventures, a garishly dressed elf bursts through the doors and breaks into a loud and boisterous song. The first few lines are in a language none of you know, but then he breaks into a chorus in common...
… the fates have come to grasp your hands,
to twist your ears and make amends
for past transgressions of ill luck and chance
that took your joy with foul circumstance.
The maiden fair, the men with two heads,
the beasts from far lands, the witch of dread,
all are here to grant you new life,
a life of mystery without all that strife.
Come to the carnival, play fate's games,
explore new sights that hail from far planes,
and learn what your life is meant to be:
You may walk away with the secrets of eternity.
As the last line leaves his mouth he bursts into laughter and throws something at the ground. It bursts into thick smoke that swirls and nearly instantly clears, but as it does he has disappeared ... although his laugh lingers on. You suddenly realize that everyone in the bar stood frozen as he sang, yourselves included. There was magic afoot here."
"As you return to town after so many weeks away you note a strange smell near the gates. It is sickly sweet and bitter at the same time, like rotten candy or decaying flowers. It takes you a moment to realize it is coming from a set of wagons parked along the edge of the road there at the city gates. An odd assortment of people and animals stand by them - a two headed male goliath carrying two huge warhammers, a dwarf female that stands nearly 7 feet tall and 5 feet wide that holds a gnarled staff as if it were a baby, a strikingly beautiful androgynous humanoid - one you think to be human at first, but revealed to be something else when their reptilian gaze focuses on your band for a moment, a horde of halflings that seem to span every stage of drunkeness, and many exotic beasts of burden.
As you're looking them over, an exceptionally tall and lean man with a bright blue top hat pushes past the tall dwarf and calls out to the odd people. 'We have our permit. The show goes on. We meet outside the Western Gate in an hour to set up the tents.'
As several members of the odd crowd disperse, the androgynous beauty catches your gaze one more time and whispers the words 'Help Me' silently to you before you lose sight of it in the crowd."