Skyrim has shipped with low-resolution versions of neighbouring regions previously seen in past Elder Scrolls games.
The secret was discovered when an explorer found a stone archway near Riften that was blocked by an invisible wall.
With some creativity, the explorer passed through this geographical boundary and into the neighbouring region of Morrowind.
There the explorer found a scaled down, low-resolution landscape, and models of Solstheim and Vvardfell.
The explorer also caught sight of central region Cyrodiil, and the Imperial City. Cyrodiil borders Skyrim to the south.
Vvardfell was the island province that The Elder Scrolls 3: Morrowind story took place on. Solstheim was a large, cold, northern island added in expansion Tribunal.
Cyrodiil and the Imperial City were part of The Elder Scrolls 4: Oblivion.
DLC foundations? Maybe. Another explanation, however, is that Bethesda included these regions to fill out the 3D Skyrim world map - offering players a zoomed out, top-down glimpse at what lies yonder.
Bethesda hasn't announced any Skyrim downloadable content. When it does arrive, however, it'll be exclusive to Xbox 360 for 30 days.