This is the 3956th most frequent German word.
unmittelbar
Direct; immediate.
Here, 'unmittelbar' is used as an adjective to describe the 'Nähe' (proximity), indicating that the closeness is direct or without anything in between.
Die unmittelbare Nähe des Parks macht diese Wohnung sehr attraktiv.
The immediate proximity of the park makes this apartment very attractive.
In this sentence, 'unmittelbar' functions as an adverb that describes the manner in which the police started their investigation — without delay.
Nach dem Unfall begann die Polizei unmittelbar mit den Ermittlungen.
After the accident, the police started the investigations immediately.
Here, 'unmittelbar' is again used as an adjective to describe 'sichtbar' (visible), emphasizing that there was no time gap between taking the medication and observing its effect.