(sorry I've been searching for days and can't find a hgss pic so this is a GSC pic from gen 2)
Route 27 is an east-west route located in extreme southwest Kanto. The route is the first location in Kanto that Trainers from Jhoto encounter . This route is one of the longest routes in Kanto history. The eastern end is at Route 26 east of Tohjo Falls. The western end is at the Johto-Kanto border, where Route 27 becomes part of New Bark Town.
Route 27 begins as a water-logged route at its western terminus, requiring Trainers to Surf east from New Bark to reach the first area of land along the route. After making landfall for the first time, a helpful Trainer near the shore will notify other Trainers that they have officially entered Kanto. The route continues east to a three-way intersection. The east path leads to the lower portion of a ledge and, ultimately, a dead end. The lack of a through route to the east forces Trainers to the north, where the path meets the western portal of Tohjo Falls.
A Trainer awaits at the eastern portal, battling unsuspecting Trainers who exit the area. Also around this area is a house owned by a woman who can detect how devoted a player's Pokémon is to them. If a Trainer shows her that their lead Pokémon is attached to them, the woman will give them TM37 (Sandstorm). South of the house is the aforementioned ledge used to bypass Tohjo Falls when heading west along the route.
The route crosses a pond before resuming its course on land. This area of the route is home to the lone patch of grass along Route 27. The path of Route 27 follows the grass southeast, passing a Trainer amongst the grass, before arriving at a bridge. There are two Trainers near the starting point, with a third, Ace Trainer Reena, on a north-south segment east of the starting location. The beginning of this segment is also the western terminus of an express path that originates on Route 26.
After battling, Reena will offer to exchange phone numbers for rematches.
East of Reena, the bridge turns east once again, becoming Route 26 eight paces to the east.
There are two water paths which are optional.
Western water path
Directly south of the west entrance to Tohjo Falls is a shoreline separating the land-bound route from a water path. The path on water turns east shortly after heading south from the shore, paralleling Route 27 to its end on a tiny patch of land containing a Rare Candy.
Eastern water path
The eastern water path is a southern extension to the large water body that encompasses most of eastern Route 27 and southern Route 26. The start of the path is at a whirlpool southeast of Reena's location. The use of Whirlpool is necessary to pass. The path then turns east, landing on an island containing Bird Keeper Jose, another Trainer who will offer to trade numbers TM02 (Dragon Claw)