Where is the fourth gym in Pokemon ruby?
The Fourth Gym is in Lavaridge City.
For Pokemon Ruby/Sapphire/Emerald, the fourth gym is a fire gym. So, train a water type Pokemon by battling against the hikers at route 112. For Diamond/Pearl, the fourth gym is a water gym, thus train a grass or electric type Pokemon on route 212. For Platinium, the fourth gym is a fighting type gym, thus train a flying or psychic type at route 214 For the rest, i won't go on.
The fourth Gym is in Lavaridge City on the most western side. The Gym Leader inside is named Flannery and she specializes in Fire-type Pokemon. Her Pokemon are a level 26 Slugma, level 26 Numel, and a level 28 Torkoal. After defeating her, she'll give the TM Overheat with an addition of the Heat Badge for your Badge collection in Hoenn.