The £2m man-made hill opened last week only welcoming those who had purchased online tickets in advance, before closing for two days later.
However, following its underwhelming launch, Westminster Council has decided to scrap the ticket price, which was between £4.50 and £8, and reopen it as a free experience.
Marble Arch Mound was commissioned by the local authority in the hope the installation would draw people back into the West End after the Covid pandemic.
But was met with derision after visitors complained they were not able to see the promised 360 degree view down Oxford Street and Hyde Park from the 25-metre viewing platform.
The town hall issued refunds for those who had already purchased tickets for the experience, and had made it free for the month of August.
Chief Executive of Westminster Council, Stuart Love, said: “We’re very sorry that the Marble Arch Mound wasn’t ready for visitors when it opened. We made a mistake and we apologise to everyone who hasn’t had a great experience on their visit.
“We wanted to open the mound in time for the summer holidays and we did not want to disappoint people who had already booked tickets.
Labour councillors have called for an inquiry into how the project “so spectacularly flopped” to ensure the “fiasco” is not repeated.
The party’s Westminster leader Adam Hug said: “There are some basic questions that the council needs to answer about what went wrong with its decision making and project management.
"These are questions must be answered now but Labour believes there needs to be an independent investigation of what happened to ensure this fiasco isn’t repeated."
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