You can make a looking glass/gliched mushroom in Minecraft, follow the simple steps below

Build a nether portal.

Enter the nether.

Find a good place where there is no fire of lava.

Dig a hole 1 block down.

Place a grass block in the hole.

Place a mushroom (brown) onto the grass block (can be dirt).

Use bonemeal on the mushroom (get bonemeal from bones).

Use ladders to climb onto the mushroom and look down.