Crowds queued for more than an hour to see the 25ft (7.5m) marionette at St George's Hall.
The grandmother figure, one of three giants who will appear in the Memories of August 1914 show, will be on show in the hall until 19:00 BST.
She will then walk through the city, along with a little girl and a dog, on Friday.
Some visitors to the hall said the giant was "lovely" and "well worth queuing up for an hour to see", while others said they were "shocked by how big she was".
One man said she was "sleeping there very peacefully with a nice smile and she's wearing her slippers".
Director of Culture Liverpool Claire McColgan said she had had an "incredible experience being here for three weeks in rehearsals" and was looking forward to the show beginning on Friday.
The giant marionettes will take in Liverpool landmarks during the show, including St George's Hall, the Chinese Arch, the waterfront and the city's cathedrals.
Royal de Luxe, the French street theatre company behind the spectacle, said they would cover 30 miles in total.
A section of the event will be dedicated to the World War One Liverpool Pals battalions and Ms McColgan said there would be "two or three moments that will make people's hearts bleed".
"The stories that the grandmother tells are incredible - the epicness of it cannot be underestimated.
"There will not be a dry eye at the final parade."
The event, running until Sunday, will end with the three giants parading around the Three Graces and sailing away on the River Mersey.
BBC News Online will be following the giants through Liverpool with live text coverage, pictures and video of events. For more details, visit the BBC's dedicated Liverpool Giants page.
About 20,000 people saw Grandmother giant's first day asleep in Liverpool ahead of a World War One event.