The Great Marsh is located in Pastoria City in Sinnoh, and has many Pokémon that can not be found anywhere else in Sinnoh. It costs 500 to enter, and you will receive 30 Safari Balls to catch Pokémon, but you can only go 500 steps before your time is over, though you can retire anytime. You are also not allowed to save here. The great marsh has 6 different areas in it, and each one of them has certain Pokémon in them, their locations changing every day. You can see random Pokémon and their locations through the binoculars on top of the marsh's entrance building at the cost of 100. In Diamond and Pearl, a boy with green hair at the start of the great marsh will give you HM05Defog, and will give you Shards in Platinum. In Platinum, there is also a girl at the entrance of the building who will give you a challenge to find and catch 5 Pokémon, rewarding you with the Matchup Checker Pokétch App.