[X] Catch a fourth Pokemon - Catching a Magnemite or other electric-type Pokemon is why you came here, there are almost certainly good options present.
[X] Travel through the Rock Tunnel - Heading to Lavender town through the Rock Tunnel is the traditional method of travel for trainers, even if it is likely to take a few days to do.
[X] See the sights in the Area - While the attractions are limited to the Power Plant, exploring its interior would be rather fun. Chansey would appreciate the more scenic tour. Wait, why are you two here?!