A 74-year-old woman was stopped from entering a new Legoland attraction because she did not have any children with her.
Staff at the new Legoland Discovery Centre in Birmingham denied Yvonne Radcliff entry due to a "no adults without a child" policy.
The Lego fan who travelled especially to see the £7m attraction called the rule "nonsense".
Legoland said it wanted to make a safe environment for children.
Ms Radcliff, from Hall Green, told the Birmingham Mail: "I walked into the Discovery Centre and a girl stopped me and said I wasn't allowed in.
"She said it's the rules and I must be accompanied by a child.
"I was shocked and appalled to tell you the truth. It's nonsense really."
The mother said she had to walk away from the attraction in Brindleyplace and go back home.
Legoland said the centres were aimed at children aged three to 10.
A spokesman said they did not permit adults who are not accompanied with children, in order to "provide a safe and fun environment" for children to play.
But they said adults were welcome at adult-only evenings.
The discovery centre opened this week and has a miniature model of Birmingham, which took nine months to build and used five million Lego bricks.