New World in the Sky / Floating City – Almost like a 4th dimension in Minecraft, you can create a new layer of earth suspended in the sky and expand it infinitely in every direction. The existing world underneath this new Minecraft world will become an underworld, shaded from the sun. You can lead your friends to believe that this world in the sky is the original Minecraftworld, then they’ll be surprised when they arrive at the boundaries and nearly go off the edge! To do this in Minecraft, simply build a one block wide high tower by jumping and placing blocks in mid air. Once you get to the desired height, use the sneak button (hold down the shift key) to ease over the edge of the tower to place blocks out in a plane. Build what you want on this floating world, including a floating city.
Long Train Connecting Multiple Villages or Cities – If you collect enough iron and gold to make powered rails, you can create a train track linking multiple villages and cities. You can also create a train station at each city, by have a switch to the powered rail, where the powered rail is down sloped, so that it automatically accelerates when activated. When deactivated the powered rail will act as a break. Build villages or cities at the stops and travel in the Minecraft wilderness between them.
Roller Coaster – Use rails and powered rails to create a roller coaster. You can even get creative and have the roller coasters fly off the tracks. Just make sure that the landing site has a downward sloped rail, so the roller coaster can continue when it lands.
Minecraft Fireworks – Create a stone tower with red stone wire and red stone repeaters spiraling up it to bring power up to the sky. Then create a maze of stone walkways in the sky with red stone wires. At the end of each stone walkway, have a block of TNT connected by red stone wire. You can even get creative and use other sources of light such as buckets of lava that fall when the TNT explodes. Make sure the source of power (red stone torch) is off while creating the set up for the fireworks. Also check to make sure that the TNT blocks in Minecraft are located away from the tower, so that setup for the next round is easy and you do not have to build the power tower again. Before you start your Minecraft fireworks show, check that your render distance is set to normal, and you are in sight of the fireworks. Obviously only do them at night!
Underwater Castle – Creating an underwater structure in Minecraft is tricky and requires planning, but the affect is worth it. Locate the boundaries of the building where there’s a large body of water. Build glass walls where the exterior of the building would be, and extend them to the surface. Make sure the walls form a closed loop, therefore isolating the body of water inside the wall. Then fill the water from bottom to top inside the walls with Minecraft blocks. They can be anything. Sand or earth works just fine. Once you filled in all the water within the walls, unbury the fill, and you now have glass holding back water. Then build a roof slightly below the water level outside. Once the roof is sealed, fill water over the roof with water buckets. Make sure you can access the inside of the building without flooding it!