Codex Sinaiticus

http://www.codexsinaiticus.org/

One of the treasures of the British Library [1] being made virtually available to the hoi polloi.  (You need to be a top level specialist to get near this outside of a display case otherwise.)

[1] TOTD recalls being on a tour of the BL several years ago and asking a senior member of Library staff about this item.  They’d not heard of it.