1. A computer implemented method for providing a cognitive tour guide service to a group of participants, comprising: collecting, by a cognitive tour guide engine running on a computer, sensory data on the participants and on environments of a tour in real time captured by two or more cognitive agents accompanying and leading the group for the tour with a present route such that the cognitive tour guide engine learns location of the group, respective pace of travel for the participants, and respective level of interest of the participants for a landmark in the present route; optimizing, by the cognitive tour guide engine, the present route by use of at least two objectives of the tour in real time during the tour, a first objective of the tour from the at least two objectives being to minimize expenses for the tour, and a second objective of the tour from the at least two objectives being to maximize enjoyment of the participants, based on the collected real time sensory data; and notifying, by the cognitive tour guide engine, the participants and the two or more cognitive agents of two or more new routes generated from the optimizing in real time, respective new routes of the two or more new routes corresponding to each subgroup of two or more subgroups formed from the group of participants based on each objective of the at least two objectives of the tour, such that the participants of each subgroup may continue the tour according to the respective new route corresponding to respective subgroups.