Rock Tunnel is the only route to and from Lavender Town. However, unlike in the games, there are guides these days who will help you make the fastest time (in exchange for P300 a person, that is!)

As for tours, those take approximately two hours... there's only so long most tourists are willing to wander around a power plant before their legs get tired or their tummies hungry or maybe they just want a nice nap!

(Also... the tour guides want lunch, too.)