True Laboratory is an optional area in Undertale, following the boss battle with Asgore and completing the requirements of a Pacifist playthrough.
Our complete Pacifist guide tells you how to get here, but in short, you need to go through the entire game without killing anything to unlock this bonus dungeon.
How to access the True Laboratory
If you made it to the end without killing any monsters (apart from Flowey) and befriended Papyrus and Undyne along the way then the story's not quite over yet, and there's more to discover.
Head back to MTT Resort and Undyne will call with a favour to ask. Get the ferry from Hotlands to Snowdin Village and go to Papyrus's house, and Undyne will give you a letter to deliver to Alphys.
Take the ferry back to Hotlands and slide the note under the door, and after a brief and awkward conversation you'll end up on a date with Alphys.
During the date it makes no difference which answers you give to any of the questions. Undyne will show up, things will get even more awkward, and you'll find yourself back in the sewer.
As you leave Papyrus will call and suggest you go and speak to Alphys again, so head back to the Laboratory.
When you arrive the place is deserted, and you'll find a note on the floor. Read it, then head through the door to the north and ride the elevator down to the bottom.
It's dark and eerie down here, but you have no choice other than exploring so head east - the panels on the wall will provide some clues as to what's going on.
When you reach the lobby at the end of the corridor you'll encounter a locked door; there are four keys needed to open it, so start by heading through the exit in the top left and follow the corridor to the end. Use the three taps to summon some Memoryheads.
Memoryheads boss battle
As with all the fights in this area, they're designed more to be creepy rather than dangerous. Call the Memoryheads on your phone by selecting Cell from the Act menu, then Refuse when they ask you to join them.
Their attacks are very easy to avoid - just stay away from the dots that appear in the combat box.
Once you've Spared them collect the red key they leave behind and head through the door to the north. Use the key in the panel on the wall, retrace your steps to the lobby, and head out through the exit in the top right.
Follow the passageway east until you come to a room with several beds in it. Examine the rightmost bed in the middle row to find the yellow key, use the save point in the corner, and then exit to the north.
Head right into the foggy room and use the switch at the end to clear the air, and Endogeny will appear.
Endogeny boss battle
This fight is very similar to Greater Dog. Start by Beckoning it towards you, Pet it, Play with it, then Pet it twice more to Spare it.
Head back out into the corridor and head west. When you come to the door in the north wall head inside and examine the bathtub at the far end to find the green key, then return to the corridor and head west again.
You'll come to a room with a rather odd looking structure in the middle of it. Head into the room immediately to the north and use your yellow key.
The room contains some video tapes that answer some questions but pose just as many; once you've watched them head back out into the main room and use the save point.
Lemon Bread boss battle
This creature is a combination of Shyren, Moldbygg, and Aaron. Start by Humming to it, then Unhug it, and finally give it a Flex, and when it attacks stand in the gap between its teeth to avoid taking damage.
Head west and you'll end up in a room full of fridges. Look at them all, and then head for the door at the far end.
Snowdrake's Mom boss battle
She won't attack you - just tell her three Jokes and the fight is over.
Pick up the blue key she drops, head through the door to the north and use your green key, then return to the room with the beds in it and exit to the east. As you walk past the mirrors Reaper Bird will attack.
Playing Undertale? Our complete Undertale walkthrough and Pacifist guide will explain how to finish the game while sparing everyone, covering all areas including the Ruins, Snowdin, Waterfall, Hotlands and The Core and more. You can also learn about how to unlock every Undertale ending and all Undertale Trophies, access hard mode and play the game in the most evil way possible with a Genocide run.
Reaper Bird boss battle
Pick On the bird first, then Pray, and finally Mystify it. Her attacks vary each round, but are all easy to dodge.
Head to the room at the end of the corridor and use the blue key, then return to the lobby - the large door will now be unlocked, so head inside.
The elevator doesn't have power, so leave through the door to the left and follow the corridor. As you approach the switch in the room at the end more creatures will attack, but Alphys will call them off. Restore the power, then return to the elevator and you'll be returned to New Home.
Head back to the throne room where you first fought Asgore. There's quite a lot of story to take in, but the pieces should all start falling into place as it builds towards the encounter with the final boss and the true ending. Very best of luck!