How Do I Get to Acuity in Pearl?

Go to Canalave City in the southwest of the Sinnoh region and take on the Pokemon Gym leader, Byron. He has a Level 36 Bronzor, a Level 36 Steelix, and a Level 39 Bastiodon; because these are all Steel-types you can beat them using Ground and Fire-type Pokemon. Bastiodon is also very weak against Fighting-type attacks.

Go to the Canalave Library just to the north of the Gym. Talk to Professor Rowan on the third floor and he'll tell you about the Legendaries at the lakes. There will be an earthquake, apparently due to an explosion at Lake Valor in the east of Sinnoh, so head there first.

Head into the drained lake area and fight your way past the Galactic Grunts who are hanging around. At the center of the lake you'll meet Galactic Commander Saturn, who has a Level 35 Kadabra, a Level 35 Bronzor and a Level 37 Toxicroak. Kadabra is weak against Bug, Dark and Ghost-type attacks while Toxicroak is weak against Flying, Ground and Psychic-types. Beat Saturn and he'll tell you that Galactic Commander Mars is at Lake Verity.

Head to Lake Verity in the southwest of Sinnoh and you'll find Professor Rowan battling Team Galactic. Battle past the Grunts and you'll meet Commander Mars, who has a Level 37 Golbat, a Level 37 Bronzor and a Level 39 Purugly. Golbat is very weak against Electric, Rock, Psychic and Ice-type attacks while Purugly is weak against Fighting-types. Now you'll be told to head to Lake Acuity.

Go to Celestic Town and put Pokemon in your traveling party that know the moves Strength and Defog. Head west onto Route 211 and continue west to Mount Coronet. Head inside the mountain and use a Pokemon's Strength move to shift the boulders so you can head north. Go north and west and use a Pokemon's Defog move to clear the fog so you can see.

Continue north out of the cave and you'll come onto Route 216. Proceed north onto Route 217, and just keep moving north until you come to Acuity Lakefront. However, Team Galactic will block your way, so head east into Snowpoint City.

Head to the Snowpoint City Pokemon Gym and take on the Gym Leader, Candice, whose specialty is Ice-type Pokemon. She has a Level 38 Snover, which is very weak against Fire-types; a Level 38 Sneasel, which is weak against Fighting-types; a Level 30 Midicham, which is weak against Flying and Ghost-types; and a Level 42 Abomasnow, which again is very weak against Fire-type moves.

Go back to Acuity Lakefront after defeating Candice and the Team Galactic Grunts will move aside to let you through to the lake.