沿岸 and 内陸: coastal areas and the interior
Compare coastal sampling and a coastal town with a journey headed inland, using the relation to the sea without fixed distance or climate rules.
沿岸 close to the sea
沿岸（えんがん） means a coast or coastal area. 「調査船は島の沿岸で海水を採取した。」 says that the research vessel collected seawater off the island's coast. 島の identifies which coast is meant.
「強い風が沿岸の町に吹きつけた。」 says that strong winds battered the coastal town. 沿岸 can describe a town on land near the coast as well as the sampling location.
内陸 toward the interior
内陸（ないりく） means inland or the interior. 「海辺の町から列車で内陸へ向かった。」 describes heading inland by train from the coastal city. から identifies the origin, and へ the direction.
「地図上の内陸地域を薄い黄色で塗った。」 describes coloring inland areas on a map pale yellow. A map color does not establish the actual area's climate or ground color.
The sea as the reference
沿岸 and 内陸 present a relationship between areas close to the sea and land farther inside from the coast. These examples do not provide fixed distance or elevation criteria separating them.
向かった in the train example reports heading inland. It does not explicitly report arrival, so the stated direction and completed arrival remain separate.
What is 内陸 contrasted with in 「海辺の町から列車で内陸へ向かった。」, and is arrival stated?
Show the answer and why
The journey heads from a coastal city toward the interior. 内陸へ gives the direction; completed arrival is not stated.