(Big ass gun)
The Schwerer Gustav was developed in the 1930s for the sole purpose of crushing Forts to the ground. Two would be built the First Gustav was captured by the allies the second Dora was destroyed by the Germans to avoid its capture.
It weighed somewhere in the area of 1350 tons (like 675 elephants) and was over 155 ft long (over half a football field) it is the largest weapon to be used in battle.
It could fire a shell almost 29 miles which is amazing since the shell itself weighed in at 10,600 to 15,700 lbs.
The barrel was 31 in in diameter.
Needless to say it was somethings of a hassle to move around and repair so it was not used to a large degree in battle but it is still a fascinating weapon.
If you want to learn more about this brute here are some links to some good resources