Seen from an airplane, the island looks like a giant spider.
Literal
Airplane [from-から] look [if-と], that island [topic-は] giant spider [like-のように] appears.
から marks the vantage point. ~と in 見ると is the conditional: 'when you look from~.' ~のように見える means 'looks like~.' 巨大な (きょだいな, 'gigantic') is a na-adjective. A vivid aerial simile.