Fill in the blank with the correct word from the options given below:

I fondly remember the time _______ my friends and I went to Rishikesh.

when

The reason for selecting "when" to fill in the blank is that it is the appropriate word to introduce a specific time or moment in the past. In this context, the speaker is recalling a particular time in the past when they visited Rishikesh with their friends. "When" is used to connect the main clause ("I fondly remember the time") with the subordinate clause that provides additional information about when the event occurred.