File:Initial Hardmode map.png

Summary
An example map just after the Wall of Flesh is defeated. Note the "V" shape of the Corruption on the left, and the Underground Hallow on the right. Within the hallow are converted Pearlstone (the top part from preexisting Ebonstone, priorly in the chasm), as well as a lot of Pink Ice Blocks in the middle.

Near the surface, spreading segments of converted rock, grass (near the jungle), and ice (both types) are noticeable. Note that snow and underground dirt (without grass) are uncorrupted.

Pre-hardmode features
As this file is linked on world, a brief description of the features may help. First, note the layers of increasing stone towards the bottom, ending in the lava of "Hell" (Underworld) and abandoned houses. Next, note the biomes: ocean and forest, jungle (including Lihazard temple), corrupted chasm, snow, desert (surface only), the dungeon entrance, and finally another forest/ocean on the end. Apart from that of the special biomes and structures, there are some floating islands, Bee Hives, and white Spider Nests. No noticeable underground desert or pyramid is present.