Ted's mom, in his dream, has a top spinning, likely a reference to Inception (2010) and the main character's tool to know if he was dreaming. The spinning top proves he is in a dream.
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When Ted looks at the Arcadian he says "Look on my works, ye mighty, and despair!" This is a line from Percy Bysshe Shelley's poem "Ozymandias."
The outside of the building where the meeting of the Landmarks Preservation Commission took place it's also the outside of Barney's building (as seen in Season 7 Episode 20)