From the author's README on Thunderstore

The Convention Center, Chase Plaza and the Seaport. Ported from Tony Hawk's Underground (2003) to ReSkate, with the original textures AI upscaled.

Pick THUG1 - Manhattan from the map list. Climbable ladders, every grind rail, native water, and fast travel points at the original teleport spots.

The pack

Every level from Tony Hawk's Underground is being ported. Install Tony Hawks Underground 1 Map Pack to get every map, or just the maps you want.

Map	Package
Tampa	Tony Hawks Underground 1 Map Pack Tampa
Manhattan	This package

The rest of the THUG1 levels are in progress and will be added here as they are finished.

Install Tony Hawks Underground 1 Map Pack Manhattan

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Tony Hawks Underground 1 Map Pack Manhattan and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.