Yes, you are right. It all depends on where you are. If you are in an inland town ( i.e. not on the coast) , you might say 'Let's go to the seaside'. And yes, this included all the facilities of the seaside resort. I live in a town which is a seaside resort, so we never say 'go to the seaside', because we already live there. We would say 'Let's go to the beach'. When you are already on the beach, sitting on deckchair enjoying the sunshine, you might say 'Let's go in the sea'. As Ruthi says, 'go to the sea' isn't a normal phrase to use. You'd only refer to the sea ( i.e. the water itself) specifically if you are already at the beach. In that case you would say 'go in the sea', which means enter the water. One more piece of vocabulary for you: in British English at least, we talk about going to the 'seafront'. This is the promenade running alongside the beach, with shops, cafes etc. - the equivalent of the Italian 'lungomare'.

We usually say "go to the seaside"or "go to the beach" which are the same.We don't usually say "I am going to the sea".

Maybe i should mention a famous old British music-hall song. Main point of course is the funny sound of the phrase "to be beside the seaside." It's not really logical to be beside the seaSIDE. The "prom" is a promenade, a broad walkway along the beach, where you might find bandstands and bands playing. To "be beside myself" means so thrilled that you are transported with delight, almost a waking out-of-body experience. https://www.youtube.com/watch?v=kcHyyuGjuk0 "Oh! I do like to be beside the seaside I do like to be beside the sea! I do like to stroll along the Prom, Prom, Prom! Where the brass bands play: "Tiddely-om-pom-pom!" So just let me be beside the seaside I'll be beside myself with glee And there's lots of girls beside, I should like to be beside Beside the seaside! Beside the sea!"

In the U.S. "the seaside" means a general region. A "seaside resort" means a town that caters to people who want to go to the beach. "The beach" means specifically an area of sand where you can spread a blanket, or walk down into the ocean. (You can also have a "pebble beach" or a "stony beach.") "The sea" means the water itself. "By the sea" means near the edge of the water. "The shore" means any dry land next to the sea. "Seaside" suggests recreation, "shore" does not.

All three actually mean the same things, although is English 'going to the seaside' flows more naturally in conversation and is the phrase that is usually used. The differences in language between Italian and English are: Sea = mare Beach = spiaggia In Italy we say 'andiamo alla spiaggia' which also means or includes the facilities of the town along the sea that we are visiting. So although a direct translation of this would be we are going to the beach, it's literal meaning in going to the seaside. Hope this helps.