。
The car got stuck in the mud.
Literal
Car [subject-が] muddy-place [to-に] got-stuck-[compound-込んだ].
ぬかるみ ('muddy place, slush') is a common noun for a soft, muddy patch — derived from the verb ぬかるむ ('to become muddy'). 填まり込む is a compound verb 填まる ('to fit into, become stuck') + 込む ('into, completely') — the 込む suffix intensifies the 'into' direction and the completeness of the stuck state. The kanji 填 is uncommon; often written はまり込む.