Step 1: Identify the institution.
The National Research Institute for Panchakarma (NRIP) is a premier centre for Ayurvedic research, specifically focused on Panchakarma, the classical detoxification and rejuvenation therapy system of Ayurveda.
Step 2: Locate the institute.
NRIP is situated in Cheruthuruthy within the Thrissur district of Kerala. It operates under the Central Council for Research in Ayurvedic Sciences (CCRAS), Government of India.
Step 3: Eliminate other Kerala cities.
Thiruvananthapuram, Kottayam, and Calicut are major Kerala cities but do not host the NRIP. The correct location is Thrissur district.
\[ \boxed{\text{Thrissur}} \]