Question

where is the 3rd gym in pokemon diamond?

Answer 1

The third gym in Pokemon Diamond / Pearl is at Veilstone City. The Gym Leader name is Maylene. Actually, you can just Googling it. It's easy to search

Comments

how can i do that googling?

---

Google is the worlds most popular search engine http://www.google.ca/

Answer 2

After you reach Hearthrome keep going untill you reach Solaceaon, there will bme a route to Veilstone gym. After that you have to go to Pastoria and fight that gym. The fifth gym is in Hearthrome.