"You hear sirens, and police cars and you just worry, you become a little uneasy, " said Linda Bensley, a 53-year-old visitor from Australia.

WSJ: Mayor Sets Precautions Following Boston Marathon Explosions

Krissada turned to Bill Bensley, a Bangkok-based American who became famous for designing plush resort landscaping in Thailand and Bali before moving to the front ranks of five-star-hotel architects.

FORBES: A Lavish Hotel Project Unites Thailand's Sukosol Family