Where is a good platform to invest in gold?

Adding on to Chris' answer, it's also possible to buy via SGX as SPDR Gold Shares (SGX: O87), should you prefer to keep your trades local. There are downsides though, such as higher commissions.

If you're referring to investing in gold through ETFs such as GLDM, you can consider any broker that allows access to the US markets. Some platforms include, TD Ameritrade, Tiger Brokers and Interactive Brokers.