Impressive Mt. Vesuvius can be seen from all over the Bay of Naples but a trip to the bay area requires a trip to the summit.
Since this volcano is watched so closely, it's very easy to reach. You can drive most of the way up the volcano, park along one of the roads and finish the ascent up. I believe it's about a mile walk to the summit.
Once at the top, you're met by some small souvenir shops, eateries, and spectacular views (of both the caldera and the bay). The caldera itself can't fit entirely inside the photos so photos of it are not nearly as impressive as the experience itself.
Steam can be seen rising from within the caldera. I've captured it on video but I'm unable to post it here. That just means that you'll have to make the trip yourself.
When you've taken in all that you can of the caldera, you can simply turn around and be stunned by the panoramic views of the entire bay. Walking around the caldera, you'll come across places to sit, buy food, and drink the tears of Christ. I suggest you do all of the above!
You'll have the option of red or white tears. Try both.