How to open the door in Scorn using the rail track and sliding block puzzle

The first Scorn door puzzle you find involves a block sliding egg puzzle and a railway track and cart to get what you need. It's long and complicated, and with the game explaining nothing, it's a hell of a challenge to drop into a cold, within minutes of starting. So, to help you get the rail cart moving, solve the cocoon block puzzle and open that door, here's everything you need to do. 

How to open the door in Scorn

You'll encounter this Scorn door puzzle when you reach a large circular chamber with a tower in the centre. If you climb this central structure you'll be able to get a bird's eye view of everything, as you can see below, to view what you need to do overall. 

The circles you can see are rail points you can interact and use to change the direction of the track running around the area, while the more stick-shaped outline near the middle/top is the cart you'll need to use. 

The objective of all this is to open this large door: 

There are two terminals here: one that unlocks the door and one that opens it. The problem is that you need to hold the key in place to get it open - as soon as you take your key out, the locks re-engage before you can hit the other switch. And, because the key is grafted to your hand, somehow you need to find another key. Or hand. 

If you've wandered around at this point you'll have found loads of machines and things you can interact with that all seem to be missing something. Ignore them all for now and take the small corridor opening immediately to the right of the main door. Follow it though and when it opens up into a room you'll find a large circular lift. 

Take that lift up to reach the area below and start the first part of solving this puzzle. 

When you get to the top, ignore all the tunnels and other routes, as you can't do anything with them yet. Instead head to the central area you can see above with two terminals. Activate the central one first and you'll see a big robot claw pick up a glowing cocoon which will fall apart. Leave that terminal and use the one on the right. 

You'll now have a sliding block puzzle to deal with in order to get the only cocoon with lights on into the position where the one that broke was, so you can pick it out. 

There are a variety of pieces to move, made of single and double cocoons, and in order to solve this block sliding puzzle in Scorn, concentrate on getting the horizontal double pieces we've ringed above into that position in the image. If you can get them all into that far right positioning you'll have room to move the single pieces past the one you need, and free it. 

Once you've got it in place, activate the middle terminal to transport the cocoon below. 

Back on the lower level find the cart and you'll see the cocoon you rescued above the machine in front of it. Use the terminal that overlooks the cart and you'll be able to move a robot claw to pick up the cocoon and move it to the cart. You'll have to 'use' the cart to make the transfer.

Now you can move the cocoon in the cart along the rail track. Push it to the hanging structure over the track that you can see on the left in the image above. Activate the nearby terminal and you'll stamp some sort of lid on to on the cocoon. 

Next push the everything along the rail track as you see it arranged in the image below. 

This will let you push it into one of the side rooms where you can find this scoop like machine: 

Push the cart into place and then use the bigger of the two terminals to control the robot arm. Again, move and position the arm and 'use' the cocoon to transfer it from the cart to the machine with scoop. When it's in place, pull the smaller switch in front of the scoop machine to scrape the creature out, leaving you with its arm. 

And you're nearly done. But before you can open the door, go back to it and take the opening immediately to the left, where you'll find another version of the machine you originally used to get your own key. Put the severed arm into it to add a key to it, and then you can use that to open the locks, leave it in place, and open the door to proceed.