City day out? This is the worst part (4)

I believe the answer is:

lees

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'worst part' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for lees that I've seen before include "Sediment from fermentation of alcohol" , "Sediment from alcoholic drink" , "Sediment that settles at the bottom of wine" , "Dregs left by eels" , "Wine dregs" .)

I've seen this clue in The Independent.

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