After retiring, they decided to spend their days beachcombing along the Caribbean shores.

beachcombing 是由 beach（海滩）和 comb（梳理、搜寻）组合而成的动词，加上 -ing 后缀构成现在分词形式。字面意思是"在海滩上搜寻"，引申为"在海滩上悠闲地捡拾贝壳等物品"的活动。