Wang Yuxia's husband once promised to take her to all the beautiful sights across the country. But when he suddenly died, it seemed her dream had died as well.
So it was up to her sons to carry out their father's promise.
Realizing their 81-year-old mother gets carsick easily and they cannot afford to travel luxuriously, they built a three-wheeled carriage to take her around the country - powered only by their own feet and the determination to express love.
"We are not doing this for money or fame. We are just spreading the virtue of filial piety," said Wang Kai, 59.
"Compared to what our mother has done for us, what we give in return is never enough," he added.
During their first trip in 2007, they spent 265 days traveling across 25 provinces and two municipalities before arriving in Hong Kong.
This time, in 165 days, the two brothers have hauled the carriage more than 4,500 km from Heilongjiang province in the northeast to Fujian province in the southeast.
Their target destination is Taiwan.
"Our biggest dream is to carry our mother around the island," Wang Kai said.
The carriage, built for 5,000 yuan ($730), is fitted with three beds, windows and heat-retaining panels to make mom comfortable.
( their routes )
The brothers named it "Thanksgiving" to express gratitude for their mother's love.
Wang Yuxia can usually be seen enjoying the sights through the windows.
"My sons have been taking good care of me on the way," she said, and the warmth of the carriage has prevented her from catching cold.
She is happy to have seen more than 100 tourist attractions so far.
"I'm very moved by what they've done. I can't thank them enough," she said.
On the road, Wang Kai pulls the carriage from the front while younger brother Wang Rui, 57, pushes it from behind
So far, they have worn out six pairs of shoes.
"I can walk 107 steps every minute and 10 hours every day, which means 65,000 steps or about 40 km a day," said Wang Rui.
That is almost the distance of an Olympic marathon.
The brothers' love for their mother has moved thousands of people.
.( Wang Kai )
In September last year, the Taiwan Sleep Disorders Association, a non-governmental organization, invited them to tell their story.
And on March 3 this year, the brothers were invited to conduct a class on filial piety at Fuzhou University.
They have already spent half of the 40,000 yuan they put together before setting out on their journey.
Supporters and admirers have been providing clothes, food, drinks and other daily necessities.
"The brothers are doing whatever they can to make their mother happy and I must do something for them," said Zhuo Feng, a resident in Fuzhou, capital of Fujian, who bought the brothers new shoes and their mother new clothes.
A number of businessmen who were moved by the Wang brothers' filial act also offered them money, but the brothers said they will not accept any cash for their undertaking.
In a letter written to his wife, Wang Rui said it is the love of their mother that has helped them conquer all difficulties.
"Making our mother happy is priceless," he said.
During their first trip to Hong Kong, the brothers decorated the roof of their carriage with four dragons to symbolize their Chinese heritage. These were later changed to doves of peace to express their desire for peaceful ties across the Taiwan Straits.
They have been in Fujian nearly a month now, waiting for authorities to approve their travel to Taiwan.
Wang Kai said all they know about Taiwan is from books, which say Ali Mountain and Sun Moon Lake are beautiful. The island's fruits are also famous, he said.
On Aug 8 last year, when the brothers heard about the earthquake hitting Taiwan, they immediately donated 1,000 yuan to the Red Cross Society of China to help quake victims.
"People across the Straits are one family," Wang Rui said.
"We are just helping our brothers and sisters in our way."