1) Paris est une belle ville. On y va pour voire les beaux garçons, pour visiter les musées, ... (Paris is a nice city, one goes there to see the nice guys, to visit musea, ...)
2) On y va = Let's go. Nous allons à Paris? Oui, on y va.
Merci beaucoup Jan Loose! In the interim (since posting my question) I discovered On y va directly translates as 'Let’s go' but had no idea it can be used to express ‘one can go there’. Thank you for your help and examples; much appreciated.
As you'll probably come across during your course, French (and actually, related languages like Spanish, Italian etc) use a special type of word-- technically a "clitic"-- for expressing certain basic functions, such as "me", "him", "about it"... and "there". These special words actually go before the verb in most cases.
The "y" here is an example of one of these clitics: it basically means "there", "to there" (it can have other meanings in more complex cases). So On y va literally means We there go. As you see, y, being one of these special clitics, is before the verb, va.
It also turns out that the verb aller has a feature that English go doesn't: that the y is more or less obligatory if you don't mention some other specific place. So for example, to say I'm going tomorrow, where I'm going is literally Je vais, in French, you'd actually end up saying J'y vais demain-- you literally say I'm going there tomorrow, even though in Engish the "there" is optional, in French you generally have to put the y in (unless you specify a place, e.g. on va à la banque = we're going/we'll go to the bank). There's the odd exception that you don't need to worry about too much for GCSE.
As a set expression, On y va! also does of course mean Let's go!.