Position and direction (w pobliżu, z tyłu, w kierunku)

Where exactly

w pobliżu — nearby; with a Genitive, near: w pobliżu dworca.

z tyłu — at the back — and z przodu — at the front. Both are z + Genitive of tył / przód, and both take a Genitive for the thing: z tyłu domu (behind the house, at its back).

w środku — inside; in the middle: w środku torby, w środku nocy.

Which way

w kierunku + Genitive — towards, in the direction of.

na dół — down, downstairs as a DIRECTION (Accusative); you already have na dole for the position. The same pair works with góra: na górę / na górze.

Beginning and end

na początku — at the beginning — and na końcu — at the end; both na + Locative, and both work for place (na końcu ulicy) and for time (na początku filmu).