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Milkshake 2

Solution: https://youtu.be/mC2oCpPjww0
(The ending is slightly different but i think you can manage)

Portal community maps have various levels of difficulty. People tend to play easy and pleasant maps instead of highly complicated ones. But the latter is much harder to create and design. Mapper needs to think about the logic of the map to have an elegant solution.
Imo the problem is that there isn't any indicator to the difficulty of the map. Test subjects can only rate the overall quality of the map. As a result, harder maps become unnoticed as only a few people can pass them.