Realistic Terrain Movement changes how movement works in Minecraft by making terrain, altitude, and environmental conditions affect both players and mobs. Roads become faster, mud and snow slow you down, mountain winds become a challenge and the open ocean is no longer a safe place for small boats.
The mod is designed to encourage players to use transport mods or other environmental mechanics.
All mechanics are fully configurable and can be enabled or disabled independently:
.../config/realisticterrainmovement-common.toml
Different surfaces affect movement speed:

Anti-Jump Exploit:
Boots Reduce Terrain Penalties:
Mobs Are Affected Too:
High-Altitude Wind System:
Above Y=120, strong winds begin to affect movement. Wind strength scales up to Y=250
Boats and Open Oceans:
Small boats are not suitable for deep ocean travel. The vanilla boat is essentially a small coastal vessel that would realistically be unable to withstand the rough conditions of the open ocean. This encourages players to build proper seafaring ships from other mods for exploring distant islands and continents.
The default configuration includes support for:
May conflict with mods that modify the MOVEMENT_SPEED attribute, apply custom movement mechanics or alter vanilla boat behavior. Also, if the transport mod you're using has the "boat" tag, it will break in the open ocean just like all vanilla boats. The solution is to disable the boat breaking feature in my mod's configuration.
As this mod was created primarily to supplement other mods, I recommend the following ones to fully unlock 100% of its potential:
Technical Notes:
EntityTickEvent.Post.MOVEMENT_SPEED attribute modifier (ADD_MULTIPLIED_TOTAL). While airborne, the last grounded value is held (sticky) instead of resetting to neutral.modid:block or #modid:tag syntax — if that mod isn't installed, the registry lookup simply finds nothing and the entry is a no-op.