Did you know with World Edit (SSP or SMP), you can create cobblestone stairs (And wooden too, I think) with a hexadecimal value of 4. This creates a block with the same attributes of air, but a solid state, and light will not pass through it. It has the cobblestone or wood break texuture just like stairs. You can walk and see through it.
I'd just though I'd share this since I found it was pretty cool. I used these WE commands:
//pos1
//pos2
//set 67:4
This would make a block of the substance, how large depending on your cuboid selection with //pos1 and //pos2.
Don't forget, You need a third party program to mod the hidden block in, but you don't need any mods to view it. It's kinda like the giant spawner's. You can only get them in via MCEdit.
I'd just though I'd share this since I found it was pretty cool. I used these WE commands:
//pos1
//pos2
//set 67:4
This would make a block of the substance, how large depending on your cuboid selection with //pos1 and //pos2.
Try it and comment!