Necrum is the second level in Oddworld: Abe's Exoddus.
As soon as you land and walk to your left, you can enter a secret area.
Secret Area 1:
Jump to the smaller platform and run to the platform you jumped from. Be sure to jump so you hang onto it. Let go and you will fall onto another one and then drop into a well. You will be dropped into the Slig Barracks. Jump so you get behind the pipes, so Sligs cannot hurt you. Run onto the next platform and go to the next area. Roll behind the pipes carefully and then climb to the platform above. After passing through the Sligs, you will find some Mudokons working under a drill which slowly makes its way towards them. Get them all to follow you and stop them just before they reach the mines. Fall down and deactivate the mines. Afterwards, rescue them through the portal. Exit through the well.
Make your way past the platform that the secret area was and climb up. Drop into the well. Make your way to the right and use the pad to bring a portal. Use the portal to get across. Go through and use the well.
Roll under the broken log and drop to the platform. Drop down and make your way towards the 4 platforms and use the pads. After using each one, a flame will be lit. Using all 4 pads will light all four flames. Afterwards, go back to the doors. Enter the top door which will open. Use the pad which will open the door and go through it. Using the bird portal will get you back to the drunk Mudokons. After exiting through the bottom door. Go through the bird portal. After exiting, follow the path to the door. After you exit the door, climb up and go to the next area. Drop down and then again get down from the platforms. Before you reach the last one, you will see two Fleeches sleeping. Drop down and run into the well. When you land, break the Spirit Lock to open the door. After it unlocks, go through it.
Afterwards, you will get into a series of trials with Fleeches. There will be levers and handles that you will need to activate in order to unlock the exit door. After completing all four of them, you will exit through a door. Drop down the platform from your right. That will allow you to rescue the Ringed Spirit and gain the Invisibility Power. By chanting you can activate it, however it will not last forever. Use it as soon as you drop to the lower platform. Make your way towards the top again and go through the door that is below the door you came into from.
Go to your left and into the door. Jump across and use the bird portal to go to the opposite platform. After that use the well to go to the platform behind. You have two choices. You can either go to the Mudanchee Vaults or you can go to the Mudomo Vaults.
When you select one of the two Vaults, before you use the well which will get you within the locations, there is a secret area. Roll to where the bottles are and use the portal to enter.
Secret Area 2:
While you are hanging, wait for the Slig to turn. Climb up and jump down. Pull the lever and then jump across, so you hang to the platform. Sneak past the sleeping Slig. Climb up and deactivate the mines carefully while the hatches are closed. Proceed towards the Mudokons and pull the lever. Go back down and while the Greeter's laser is pointed away from you, activate the mine. Wait for the Greeter's laser to come towards you, then when its on you, walk away, so that the Greeter walks onto the mine. Make sure that you are not close to the explosion. Go to the Mudokons and make them follow you by saying "Sorry" to each one. Rescue them through the portal. Exit through the well.