At indicates in or very near a near a particular place as in “At that precise position;”, at Jim’s house.”

Your usage in this sentence is clearly meaning in the direction of the Aquarium.

You could say, I was at the Aquarium with my friends.

Hope that helps a little.

At calls for futher comment. Because it is the least specific of prepositions in its spacial orientation so it has a great variety of uses.

For example:

(Location) Points defining location

Tom waits for his sister at the bank

Sue spent the afternoon at the house

(destination)

We arrived at her house

The waiter was at our table immediately

At as a preposition of time:

We use at to designate specific times.

The train is due at 12:15 p.m.

As a preposition of place:

We use at for specific addresses.

Meet me at 35 West Main St.

Maybe this helps:

Prepositions of Location: in, at, and on

and No Preposition

IN

(the) bed*

the bedroom

the car

(the) class*

the library*

school*

AT

class*

home

the library*

the office

school*

work

ON

the bed*

the ceiling

the floor

the horse

the plane

the train

NO PREPOSITION

downstairs

downtown

inside

outside

upstairs

uptown

The sentence as written means that you and the others mentioned headed directly toward (or in some other way as to cause a collision or meeting) the aquarium.

I think the point that everyone is making is that it is more likely that we would describe a visit by using to rather than at – at implies something different or dumb!

The verb “Go” is used with preposition “to”, when you mean that you reached somewhere.

There is no reason for that, just because native speakers say so, you should follow them.

When you’re unsure about using a certain preposition simply lookup the verb from your dictionary, there you can find the correct prepositions for correct purposes.

More examples:

1-going to the gym

2-going to the airport

You can say that you studied at the Aquarium but you went TO the aquarium.