Favourite eldritch abomination?

[Froge]

What's your favourite eldritch abomination? Can be from any book / film / game / medium of entertainment, etc.

For me, I would say Walpurgisnacht. It has a very nice aesthetic design and can be attacked through conventional means, such as with guns, but it is thoroughly unkillable. It has a very interesting laugh (it makes interesting bell / wind chime sounds in general) and is just generally a really disturbing / crazy thing.

The town of Silent Hill is a close second.

[Alardem]

The eponymous house from the pretentious novel House Of Leaves. The sheer bizareness of the endless staircase, the invisible demon lurking within, its ability to change dimensions whenever the author deems it scariest - it can make Silent Hill seem pleasant.

For the internet kids, it's also likely the inspiration for SCP 087 AKA the endless staircase.