Bedrock
Bedrock is found inside your starters island it marks your spawnpoint when you go to your island. It is a unbreakable block that you normally can't obtain.
History
Bedrock Stayed Unobtainable until the admins released the Dwarven Mines Update and revamped the mining system making it allowed to break Portal blocks, End portal frames, bedrock, barriers, command blocks basically anything. The admins patched the glitch very fast but even with this, it was wide known. After this there was another barely known method but the same item was obtained. The original text on the bedrock was "Please contact Jayavarmen#8817 and explain how on earth you got this item, tyvm" and then they changed it to "Well I guess you have this now.".