The Delirium Archive was a museum which took up most or all of an asteroid. It was the final resting place of the Headless Monks. The Eleventh Doctor said it was "the biggest museum ever". It was implied he visited often and used it to "keep score".
River Song deduced that eventually, the Doctor would at some point end up at the Delirium Archive and find the Home Box of the 51st century Category 4 Starliner Byzantium. She left a graffiti message in Old High Gallifreyan on it, asking for his help. Roughly 12,000 years later, he did. (TV: The Time of Angels)