From Bulbapedia, the community-driven Pokémon encyclopedia.
Route 28 is a east-west Generation II-era route located in west Kanto and east Johto. It is the only route in Pokémon history that enters two regions, although the Johto portion of Route 28 is officially named Silver Cave. The eastern terminus is at the Pokémon League Reception Gate outside of Viridian City, Kanto, where Route 28 connects to Route 22, Route 26 and Victory Road. The western terminus is at the entrance to Mt. Silver in Johto. Route 28 is the last Route able to be traversed in the Generation II games, following a player's conquest of the eight Gym Leaders of Johto, defeating the Pokémon League, obtaining the badges from the Gym Leaders of Kanto; and obtaining the permission of Professor Oak.
From the Reception Gate, Route 28 heads southwest, passing through a gap in a ledge before turning west into a strip of grass containing wild Pokémon. The narrow strip, bordered at points by a pair of small ponds, turns north after passing a small pond to its north. Route 28 forms an upside down "U" at this point, returning west at the other end. The path of the route continues through a series of intermittent grass patches before turning southwest as the route enters Johto.
The route turns west, then northwest as it approaches one of the few rural Pokémon Centers in Johto. The route continues northwest along the bank of another pond (which separates Route 28 from a small area of the route) before turning north to meet the entrance of Mt. Silver.
Pokémon Center area
Trainers who can use Cut can head east of the Pokémon Center onto a private northern path. After removing two trees, access to a house along the path is unhindered. In this house is a reclusive trainer (most likely the same trainer from Route 16 in Generation I and Generation III) who will give trainers TM47, Steel Wing, in exchange for keeping her whereabouts under wraps.
The route continues east past the house to a dead end, where a carefully-placed hidden item can be found.