Firstly, ~と言えば literally means "~ speaking of", but there's an idiomatic usage where you use it to present things that are typical, are representative, or come to your mind in regards of ~. For example:
Literal translation: "Speaking of Spain, paella and bullfights."
What it really means: "Paella and Bullfights are typical Spanish things."
I think this is the usage in your sentence. So, if the sentence starts 日本の名所といえば, what I expect would follow are things representative/typical of famous places in Japan. One of such places is the 温泉.
As regards も, here it is signalling that there are other (unmentioned, or perhaps mentioned previously in the conversation) 日本の名所 besides 温泉.
Finally, as you noticed, ~ことができる means "to be able to ~", so the negative form would mean "not to be able to ~" or "can't ~". For this reason, 忘れることはできません can be translated as "[We] can't forget".
All in all, I would translate it as
Onsen is another famous Japanese place we can't forget about.
When it comes to Japanese famous places, we can't forget about onsen, either.
Whatever clicks better for you.