But when her mother, Kate McCann, went to check on Madeleine and her younger twin siblings around 10 p.m. on May 3, 2007, what she discovered turned the family's dream vacation into a nightmare -- one that's continued for a decade.
Just days shy of her fourth birthday, the British girl had vanished without a trace from the home her family was renting in the Algarve region of Portugal's southern coast.
Since then supposed sightings have come in from across the globe -- from Europe and Morocco to Brazil and New Zealand. A few suspects have even been named and investigated, but the search for Madeleine continues.
After 10 years, here's what you need to know about the case.
' ... It just feels stolen'
Speaking just days ahead of the "difficult" anniversary, Madeleine's parents -- Kate and Gerry McCann -- tried to put into words the range of emotions they have endured over their decade-long ordeal.
For Kate, who revealed that she continues to buy birthday and Christmas presents for Madeleine, there is anger and grief at what was taken from them. In just a few weeks, Madeleine would be 14 years old.
"I mean, it's time that we should have had with Madeleine," said Kate. "We should have been a family of five for all that time. And yeah ... It just feels stolen."
But the couple also stressed their determination and hope that the current inquiry will provide them with long-awaited answers. They also reaffirmed the belief they say they've always held -- that Madeleine is still out there, alive.
"No parent is going to give up on their child unless they know for certain that the child's dead," said Gerry. "We just don't have any evidence."
A case amplified by technology
Authorities often say the first hours after a person goes missing are critical to the investigation. In this case, the evidence uncovered at the time has not answered questions about Madeleine's fate -- at least not yet.
But examining what happened in the hours and minutes after Madeleine vanished does help to explain why, after 10 years, this case still has our attention.
Madeleine's 2007 disappearance coincided with explosive growth in the prevalence of mobile phone cameras. At the same time, high-speed internet access and Facebook were beginning to connect the world like never before.
"She was arguably the first missing child case of the internet era," Clarence Mitchell, a longtime spokesman for the McCann family, told CNN in a recent interview. "Within minutes of her going missing, relatives were able to send high-quality video of her -- posting them on websites, Facebook pages and sending them to news desks."
All of this helped drive immediate public interest in the case -- interest which has endured for a decade.
'We still don't have definitive evidence'
Since Kate McCann first raised the alarm that her daughter was missing, the ensuing search has involved investigators from the UK, Portugal and other agencies around the globe. Today, London's Metropolitan Police still has a dedicated team of four detectives working the case, in conjunction with their Portuguese police counterparts.
Days before the 10th anniversary of Madeleine's disappearance, Met Police Assistant Commissioner Mark Rowley stressed in an April 25 interview that his team is dedicated to finding answers, even if concrete ones remain elusive.
"It's unusual to have a case like this where you're doing a missing person investigation where 10 years on, we still don't have definitive evidence about exactly what has happened." said Rowley. "And that's why we're open-minded, even though people are pessimistic about the prospects, because we don't have definitive evidence of what's happened to Madeleine."
Scope narrowed, but still no charges filed
In the days and then months after Madeleine vanished, Portuguese police focused their attention on a few "arguidos," or suspects -- Robert Murat, a British man living in Portugal, and then later, Gerry and Kate McCann. But the cases were eventually dropped, and all three later secured monetary damages and apologies from a number of UK media outlets.
In 2013, British police released sketches of potential suspects
and in 2014, police said they were searching for a man who assaulted five British girls on vacation in the region. But 10 years on, no one has ever been charged.
Since the Metropolitan Police began reviewing the case in 2011, Rowley said his team has combed through over 40,000 documents -- the cumulative work of the Portuguese police, who led the early stages of the investigation, plus the research of several private investigators and leads generated by numerous appeals to the public. Out of that, thousands of leads were generated, allowing Rowley's team to narrow the scope to around 600 people deemed "interesting to the inquiry."
"That doesn't mean they're all suspects, but people who were suspicious at the time or have got a track record which makes us suspicious about them," said Rowley.
As the investigation -- officially called Operation Grange -- enters its 6th year, around $15.7 million has already been spent on the search for Madeleine. In March, the UK's Home Office approved $103,000 to fund the inquiry through September 2017
, and despite the sizeable price tag, Rowley said the funds are money well spent.
"We've sifted out many of the potential suspects ... and where we are today is a much smaller team focused on a small number of remaining critical lines of inquiry that we think are significant," he said. "If we didn't think they were significant, then we wouldn't be carrying on, but we think they're significant."