"Examine the base of the monument" is a mission objective in Sequence 5 / Memory: A Room With A View
Walkthrough[edit]
Use the Rope Launcher to zipline over to the corner of the building between the Dentist/Tea Importer and the Bankers Money Lenders building. This will put you in a great position to slip through the crowd or to thin out the police keeping the crowds at bay.
You can dive into the haystack easily from here without being noticed. Or, you can use your Throwing Knives from the building above to eliminate the Police holding the crowd back. The crowd will move forward and make it easier for you to reach your destination at the front of the monument underneath the stage.
If you dive into the hay, just wait for the nearby police to be looking away. Exit the haystack and sneak underneath the stage. Do not stop for any reason.
Once you are under the stage, it breaks most lines of sight and you should be able to interact with the object there. Evie will place the disc she found in the Kenway manor in the circle and this triggers something at the top of the monument.