Back to the Portal


Back to the Portal is a Portal 2 time travel map created in three weeks using the Hammer World Editor. My personal goal for the project was to create an innovative and fun Portal level while also learning how to use Hammer during the development process.


  • Created in three weeks
  • Custom Hammer map
  • Custom visual scripting
  • Based on a time travelling mod made by Austin House

Getting Started

The gameplay part of my map was supposed to be ready for testing within two weeks, so I decided to initially prioritize function over form and then move on to the looks and feel of the level. To make things a little easier for myself in the beginning, I started out by creating a map using the in-game tool for creating maps before I decompiled it and took a look at it in Hammer. This gave me an idea of how Valve made their levels and it also gave me a starting point that I could use as a form of white boxing in my level.

Once that was done, I tried to create some basic functionality for my level such as a button connected to a door, a trigger that activated a sound e.t.c. Then I moved on to creating my time travel machine using Austin House's maps as a reference point so that I could make sure this project was possible to complete within the short timespan I had.

After that, I started to make top-downs of the puzzles I wanted to incorporate in my level. I knew I needed to introduce the player to the rules of my time travel mod while at the same time challenging the player by creating complex puzzles. Balancing the two proved to be difficult but, using the feedback given to me by the Steam community and my class mates, I was able to polish my puzzles and my environment to a point where I felt satisfied with the results.

Taking a look at how Portal 2 map editor levels are made

Trying to connect a button to a door.

Introducing a Time Machine

The first puzzle has two buttons in it which are connected to a door. The player will soon realise that this puzzle is impossible to solve and start to look around the level for ways to get out of the room.

After the player finds the exit through a ventilation shaft in the corner, he or she will get to a file room with a copying machine in it and from there the player will find the hallway which leads to the first time machine.

Hopefully, this segment will make the player feel like he or she has escaped and managed to infiltrate the facility, but also leave them wondering if the whole thing is staged and part of the test.

A "secret" ventilation shaft

Selling the illusion

In the Hammer editor, the time machine is nothing but a teleporter that takes the player to a different room, that looks the same as the first one layout-wise, but is overgrown and looks older aesthetically.

In the game, the illusion of time travel is sold to the player using some camera shake, some fade-in and fade-out effects, but also through the placement of the teleporters. When you teleport through time, the player position and rotation remains the same but the portal changes position. This makes the transition between time and space seemless and smooth.

Just in case the player didn't understand that the two rooms were one and the same, but set during different times, I also shaped the rooms in a unique and recognizable way as well as place a poster in the same spot in both rooms which read "REMEMBER! If a future you tries to warn you about this test, DON'T LISTEN".

The past...

...and the future.

Texture Change = New Puzzle?

Initially, the room in the picture to the right had working portal surfaces in both time periods but I later replaced them in the future room to some non-portal surfaces. The player had to then figure out that he or she could place portals in different time periods and walk through them in order to solve puzzles. This puzzle therefore served as an introduction to the rules of the time travel mechanic.

When the player has solved this puzzle, he or she will get to a hallway behind a door and the player will be presented with an open door to the left. At first, I left this door closed, which led a lot of players to the right, passing by the door to the left. The door on the left leads to a lab, which in turn leads to the room with two buttons and a door that we saw in the beginning of the level, except we get to see what that room looks like in the future (shown below).

Teaching the player time travelling rules using puzzles

The beginning and the end of the level takes place in the same room but in different time periods

Follow the Crow

In order to lead the player towards the final room (above), I placed a trigger right outside the room in between (right) that set off a crow sound coming from within the room.

In case the sound didn't catch the player's attention, I also opened the door fully. I did this because I had learned in a psychology class that people have an instinct to peek through open doors and their attention is often drawn to movement.

If the player only peeked through the door, but chose not to go in to the room, he or she will most likely still keep that room in the back of their mind knowing that room is where they are most likely supposed to go.

Entering the open door

Once the player enters the room, the moving rain animation will hopefully draw the player in and call on the player's exploration instincts. When the player passes through the door, a crow will fly from the corner of the room to the left where I want the player to go. This will take the player to the final room in the level.

The crow animation was originally created for use in the Portal 2 campaign, which meant that the crow was only able to fly in a few different directions along pre-determined paths. Luckily, one of the animations just so happened to fit perfectly into my level, guiding the player towards the next room and so I felt I had to use it.

The crow flies into the room I want the player to explore

The Main Puzzle

Once the player has reached the final room, and realised that he or she cannot progress further, the player can then backtrack to the hallway mentioned earlier. Here the player can enter the room to the right of the hallway and notice that it contains the main puzzle of the level. This puzzle is solved by first placing a portal on the tilted wall in the corner and then going back in time to place a portal on the floor in the past. The player can then use the momentum gained in the past to jump over the acid water in the future. When the cube is removed, the laser on the wall will activate a bridge that will enable the player to walk back across the bridge.

One portal on the tilted wall in the future...

...and one portal on the floor in the past

Once the player has obtained the first cube, he or she can take that cube back to the past, place it on the button to turn off the mancipation grill and take another cube. When the player has both of the cubes, he or she can move them to the final room where the cubes will be placed on both of the buttons and the final puzzle will be solved.

Taking the cube

The end of the level

Closing Thoughts

Given the time I had, and the fact that I had never created anything using Hammer World Editor prior to this project, I felt satisfied with the results. Thanks to my classmates, I learned so much in so little time and, when I got stuck, they were always there to help me out. Given another week, I would have made a few changes based on player feedback. For instance, I would have made the distance between the different rooms a lot shorter, since they felt a bit too long for a Portal level. I would have also liked to build a rat man hideout complete with paintings and radios. A lot of players, including myself, appreciate those rooms.

Playthrough and Solution