As most know, Bangkok downtown is the area covered by the skytrain (BTS) and the underground (MRT), especially the triangle between Siam, Asoke and Silom. This is because the most important business centers and malls are around here. But also because with the well-known traffic of Krung Thep the MRT and BTS makes the difference.
49 percent of the condos can be legally owned by foreigners, and the units are clearly identified for this, making the investment absolutely safe. Also, for a asian capital like Bangkok, prices are still relatively low (according to almost all the opinions) and very far from Singapore, Shanghai, Hong Kong but also other city where speculation is going on.
Last but not least, the AEC (Asean community, equivalent to the European Community) is quicky growing as a strong economic reality, and Thailand is one of the key player in this region and alliance.
Have a look at independent opinion about buying a condo in Bangkok. This is an example: Neil McDonough blog but if you prefer make a wide search between market analysis and forums, and you’ll be easily convinced.