Zhang and Hou focused on their careers and grandchildren until recently.
Hou watched their newborn grandson while Zhang first explored Europe in 2012, even though it was his dream to take her to the Eiffel Tower and Coliseum.
He'd often meet elderly couples on the road.
One day in Switzerland, a local couple asked Zhang where his wife was by pointing at his wedding ring and his empty passenger seat.
Zhang pantomimed to try to explain she was raising their grandson, as Chinese grandparents traditionally do.
The man then pointed at his wedding ring and watch.
Zhang understood - they should be traveling together.
"I know he meant we don't have much time left, so we must cherish it," Zhang recalls.
Two year later, the couple was on their way to Europe when the accident stopped them in their tracks. The following year, they hit the road again.
"The sceneries are endless," Hou says.
"Our home on wheels enables us to go where we want and when we want. We constantly have new neighbors."
