In just four days it's probably best just to focus on St. John's and the Avalon Peninsula. There is lots to see and to do.

Check newfoundlandlabrador.com/PlanATrip/WhatToDo/…

I agree with the other writer that there is lots to see and do to keep you busy in and around St. John's for four days (Signal Hill, Cape Spear, The Rooms), but if you do decide to get out of the city, I would suggest going to the Trinity area for a night or two. Stay at (or at least eat at) Fishers' Loft - it's a beautiful serene place with fabulous food. And the town of Trinity itself is really interesting; if the Pageant is still going in October, it is great.

When we were in Newfoundland a few weeks ago, we talked to people at the B&B we were in who said they had been to St. Pierre and it was not worth the trip - little to see or do.

tripadvisor.com/Attractions-g154964-Activiti…

This is from this forum...check it out there might be suggestions you might like to do.

Another neat little town is Brigus on Conception Bay. Stay at the Seacliff B&B. Or south to Witless Bay/Bay Bulls (only an hour drive south of St. JOhn's). We stayed at the Bear Cove Inn. Lots of whale watching/puffin tours. Beautiful section of the East Coast Trail south of Witless Bay. Drive another hour south to Ferryland so see the archeological dig site (somewhat interesting) and hike up to the lighthouse for a picnic served to you overlooking a beautiful seascape. Very unique.