It is not easy to go to Ferapontov on your own. Although there are three buses daily from Vologda (direction Lipin Bor and Petrozavodsk), you have to walk around two kilometres from the bus stop. And the bus back to Vologda is either after 1-1.5 hours (hardly doable unless you are a very good walker) or after about 9 hours and the latter means long time of waiting in the middle of nowhere or trying to hitchhike (what I did successfully).
The monastery of Ferapontov is the only one of many famous temples nearby that was inscribed as WHS. One of the reasons is that it is preserved with almost no changes since its creation in XIVth-XVth centuries. The monastery hold the masterpiece of Russian religious art - frescoes of Dionise, who is considered, after Andrei Rublow, second most important icon painter (or, as Russians say, icon writer). The frescoes are very well preserved, although constant restoration is going. Before going to the church you have you watch a short movie about the frescoes and their difficult restoration (scientists search original components of the paint, sometimes including gems). The movie is in Russian, I am not aware whether they have an English version.
Beside the frescoes, it is worth visiting two remaining tserkvas and a small museum of icons (with much more interesting examples than many ones in the churches of Golden Ring).
By the way, being in Vologda you cannot miss the beautiful St. Sophia Sobor. It has the biggest wall covered with frescoes in whole Russia and - which is extremely unlikely for this country - taking photos inside is available without limits.