Across the road from the Mount Pleasant postal depot is the Postal Museum. Also across the road from Mail Rail, it tells the story of the postal service in the UK.
There are a lot of exhibits, going back around 500 years. The first exhibits you come across are the wall boxes on the side of the courtyard.
The London Ornate Box was a result of a competition. However the designers initially forgot to include a slot through which to post the letters.
An Air Mail Pillar box was painted blue and had two plates with details of collection times and charges.
There are a number of postal delivery exhibits, including a Post Bus used in rural areas.
Combined with Mail Rail, this is well worth a vist, and is located only a short walk from Farringdon and Kings Cross stations.