I have a nice base on a survival world, and I want it to stay that way. Most of the base is underground (all the way to bedrock), so you don't see it right away. The part you do see when you first join the world is what I have built on the on the surface, so I want that to be presentable.

So how can I help my friends get the trampoline achievement without leaving an eyesore of a high dive platform in the middle of my base?

The answer is simple, a temporary tower.

Using the game mechanics to my advantage I set up a place where a tower could be constructed, the achievement could be earned, and then the tower is removed. All in less than 2 minutes.

Impossible you say?

I say nay nay.

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There are 2 different behaviors of blocks in Minecraft.
1) Solid blocks are any sort of block that will stay where you put it regardless of what happens around them ( dirt, stone, wood, etc).

2) Fluid blocks will fall unless supported underneath (sand, gravel). If the fluid block lands on another block it will stop there. If however the fluid block lands on a torch something very interesting happens. The fluid block breaks making room for any fluid blocks above it to continue falling.

These different behaviors are what makes this temporary tower work.

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Step 1: How It's Made

Set up a few slime blocks

One block from the slime blocks, Place down one torch

Cover the torch with one solid block.

Build up from the solid block with 2 stacks of fluid blocks. I used sand so from now on that's how fluid blocks will be referred to.

Step 2: Just Keep Building

Once you run out of sand you will be 129 blocks up in the air, plenty high enough to bounce off the slime blocks and get the achievement.

As a nice finishing touch you can put a solid block off to one side of the tower. A smart choice is to put it on the side of the tower that has the slime blocks. This block will stay up in the air after you are done. When the next person needs to use the tower they will know they are in the right spot when their temporary tower lines up with this floating solid block.

Step 3: One Small Step

Now you just take a step off the platform and fall all the way down to the slime blocks below.

And bounce ....

And bounce ...

And bounce..

And bounce.

OK .. that's enough bouncing.

Step 4: Putting Your Toys Away

Now to take it all down.

Simply break the solid block at the base of the tower.

All the sand will begin to fall down.

As the sand block hits the torch the block breaks.

Once all the sand has fallen you simply collect it up from around the torch, replace the solid block above the torch and put the sand back in the chest so it is ready for the next person who wants to use it.