This is the Jelling Stone, a chunk of rock covered in colourful patterns.
It's a short walk from Camden Town and right next to Regent's Park, yet we'd be surprised if one in a million tourists ever discovers the mysterious object.
It's worth seeking out, especially if you're Danish. The Jelling Stone is an exact replica of an ancient monument of the same name in Jutland. The original dates from 980 CE, and was erected by King Harald Blue Tooth, grandfather of King Canute and the butt of anachronistic tech jokes.
The stone in Denmark has lost its colour, but our version is picked out with primary colours.
On the off-chance you've forgotten how to read Viking runes, the inscription translates thus:
'Harald King made this memorial after Gorm his father and after Thyra his mother: that Harald who won for himself all Denmark and Norway and made the Danes Christians.'
Even if you can't read the symbols, you can tell this is a Christian monument if you peer round the back. Here you'll see a striking representation of Christ on the cross.
It's quite a treasure, all the more so for its seeming obscurity. It has stood here for over 60 years, erected in 1955 to coincide with a V&A exhibition of Danish arts and culture.
How to find the Jelling Stone
The peculiar rock can be found along the north-eastern fringes of the park, on a stretch of Outer Circle lined with extremely posh housing.
Look for the Danish church. It stands within St Katharine's Precinct, a religious enclave descended from a church that once stood beside the Tower of London (hence St Katharine Docks).
Walk past the sports cars and you'll spy a row of arches to the right of the church. Duck through these and here you will find the mock rock.