go to, visit
Every summer we went to the seaside for two months.

resort, town, village
holiday (BrE)
postcard

at the seaside
Summers were spent at the seaside.
a day out at the seaside (BrE)

by the seaside
They have a cottage by the seaside.

a trip to the seaside

Seaside is used with these nouns:
home, hotel, resort, town, villa, village