We arrived in Mexico City early this morning after three very tiring flights and an extensive tour of the Spanish airports! We have put the day to good use though and feel just about ready to collapse (after we have negotiated our way round the Metro back to our hostel!). Our plans to spend time in the Zocalo - the main square (where we are staying) - were quickly thwarted when we realised all the surrounding streets had been closed due to a manifestacion (politi...