Route: Couple of options.
- PDP route.
- PDP route to save glitch, then place a portal on that invisible box floating in space, then place it under the fizzler. Back up slightly to open the elevator, then ABH in.
- Grow wings and fly to the ledge of the observation room window. If someone can land on that ledge with ABH and some kind of voodoo magic, IMMEDIATELY QUICKSAVE. I don’t care about losing the 0.5 seconds from save penalty, we save at least that much getting to the portal gun. I highly doubt that landing on that ledge is possible, but if it is we need to make it happen. Perhaps try using the edges of the door to get a small ABJ launch?