Where can I get a 30-day extension for my tourist visa in Bangkok?

To obtain a 30-day extension for a tourist visa in Bangkok, you should visit the Chaengwattana Immigration Office, specifically Counter J. Alternatively, you can also go to the Thai Immigration Bureau at Muangthong Thani, where the contact number is 02 000 1178. Keep in mind that the extension process location may depend on the type of visa you hold, not necessarily your residence address.