I used to underexpose Velvia 50, rating it as ASA 80.

A few years back I lived near a great wood that was on a hill and around 5pm or so the light was almost horizontal and golden. I used to like make photos of how the light fell on the sides of trees and on the rocks. I'd always expose for the light and this, coupled with the underexposure, would plunge the shadows into deep black. The result was almost abstract and the way sections of the woods were rendered a deep gold whilst other parts were pure black was really great.

Sadly, I've never found a location like that where I now live.