According to constitution, person has the freedom to go wherever he want. Article 21 talks about Right to Life and Personal Liberty according to which unmarried men and women can go in a hotel room whose age is above 18 years, but they can go with each others concent. It is not illegal to visit hotel without marriage for people above the age of 18.
Constitution gives the right to stay freely in a hotel. Moreover, Hotel Associations of India considers that there is no law that can stop the girl and boy to book a hotel room but they both requires an ID proof for a security purpose.
They can build an adult relation but it is considered as a crime to do so at a public place. However, Hotel room is not a public place.
Then why police raid at a Hotel ?
There may be two reasons for this question.
1. First reason may be that prostitution is crime in India. So, they may get a tip from someone that prostitution work is going on in that Hotel.
2. Second, they may get a tip from anyone knowing that criminal is hiding in the Hotel.
If you are catched by police without any crime, then you just show your ID proof, where your age is mentioned. Then, police cannot say you anything and you can stay freely.