The clue tells them to drive to the Ford Proving Ground in Belgium to find the next clue, with Marcus telling us that being out in front means they have to work twice as hard - especially because Ernie & Cindy and Jeremy & Sandy are hot on their heels.
Back at the bodybuilding challenge, Andy & Tommy and Bill & Cathi are both giving it another go on stage, and both impress the panel enough to earn the 12 points needed to move on to the pitstop.
Ernie & Cindy, meanwhile, are the first to arrive at the Ford Proving Ground and find a roadblock waiting. One team member gets to suit up and take a new Ford Mustang through a series of manoeuvres - a speed task which involves stopping at a designated spot, a slalom course within a set time period, and a double victory donut.
Ernie takes to the course while Cindy wonders what happened to Marcus & Amani, who had been in front of them, not knowing they've lost time after stopping for directions.
Back at the pitstop, Andy & Tommy and Bill & Cathi (who had assumed it was the the end of the road for them) have just discovered the race is still on.
Over at the race track, Ernie's the first to take to the course and later tells us that he must have done the slalom challenge about 15 times before getting it right. Jeremy's also on the course at this stage and clearly having fun with the tasks. Ernie is the first to finish, although Jeremy isn't too far behind.
It's off to the town of Gent for the two teams to find the next clue as Marcus & Amani and Andy & Tommy arrive at the course, and it's Marcus and Tommy who get behind the wheel (although Andy admits he's feeling a bit jealous). By the time they've both finished the roadblock Bill & Cathi are only arriving.
The earlier teams, meanwhile, have arrived in Gent to find a detour - water or waffles. In the former they have to build a floatable raft and search a water way for two clues to piece together, while the former involves erecting a waffle stand and making and decorating 18 perfect waffles.
Ernie & Cindy and Jeremy & Sandy both opt for the waffles, but Marcus & Amani go for water after seeing them having a "hard time" perfecting the treats. Andy & Tommy also opt for water and are so quick at assembling their raft, they've already found both clues before Marcus & Amani have finished building theirs.
Ernie & Cindy are also pretty quick at the waffle challenge, so it's off to the next clue destination - Muur van Geraardsbergen - for both them and the snowboarders, who have jumped to second place. "We nailed the raft!" shouts a gleeful Tommy.
Bill & Cathi, meanwhile, are the last team to arrive at the detour and choose the waffles - until they encounter Jeremy who tells them it's a tough challenge and they decide to switch... He's not wrong. After asking the waffle judge to assess their work on numerous occasions, he and Sandy keep getting told something is wrong.
Sandy's clearly getting frustrated, even suggesting they switch detour, until she eventually realises they have mixed up two of the waffle trays. "I'm glad you finally found it!" says the judge as he hands over their clue.
While Bill & Cathi are still rowing up the canal to find their clue (and chatting to the locals), the other teams are off to the next task, which involves helping a pigeon trainer release a flock of pigeons and then tracking down an address where the pigeons have flown to in order to collect the next clue from a pigeon's ankle.
Ernie & Cindy are the first to arrive at the pigeon trainer station but have difficulty with finding the address given and lose their lead to Andy & Tommy, who easily locate the address and discover the pitstop is the Atomium in Brussels. It's another first place finish for the snowboarders who also win a brand new Ford Mustang each which they can customize to their own taste and style.
Jeremy & Sandy are the second team to check-in, followed by Ernie & Cindy, who are relieved their directions mishap didn't cost them the race. Marcus & Amani are in fourth place, which leaves Bill & Cathi in clear last.
Driving to the pitstop, the grandparents remain upbeat despite knowing it's the end of the road for them. "I'm not at all ashamed of how we've done," says Bill. "I think we are both a little startled at how long we've managed to stay with it... It's been a hoot and, if anything, it's improved Cathi and mine's relationship totally."
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A small montage of clips of their best moments plays as they arrive at the pitstop in pitch blackness to greet Phil, who tells them they have proved age won't stop you doing well on the race. Cathi says that one of their major reasons for doing the race was to show that older Americans can make a contribution to society.
"We stand together, win, lose or draw, there is no reason for us to ever fall apart," concludes Bill, telling us the race was just one more chance to be with his best friend and do some amazingly special things. "I'd do it all over again."
The Amazing Race airs Sundays at 8/7c on CBS