Hey guys, I've done this instructables on my old account, Roblox Tutorials. I got a comment not long ago (like literally today) and, I decided to update it, hope you enjoy!
Step 1: Open Roblox Studio
First of course, open Roblox Studio. This step is VERY important! Be sure to enter the place you want your walkthrough brick/part.
Step 2: Configuring
So you're gonna get the model or the part out on your baseplate.
For the tutorial, I'll just use a normal part.
The first few seconds are me putting the part in the baseplate, the rest is only me configuring the surfaces, to the next step!
Step 3: Making It Actually Walkthrough
For this, it's very simple! Just select your part and scroll down in the properties, there you'll see Behavior tab.
> CanCollide ~ WHAT YOU WANT TO UNCHECK.
Step 4: Last Step!
Go to your place to test!