On the walls

Derry's walls are surprisingly wide, as you can see in these snaps.  And of course they are remarkably well-preserved, famously never having been breached despite a number of sieges - hence the name 'Maiden City' as sometimes Derry-Londonderry is called.   The walls were built by The Hon the Irish Society at the beginning of the 17th Century as defences for the early settlers from England and Scotland.

Not a sinner about the place - literally

As you walk around you can't help notice the strange little towers from time to time, like this one above.  Obviously a look-out sort of thingmy, with small openings to peer through and see if your enemy is coming at you with a loaded musket, or whatever they had to throw at you in those days.  The one above is just opposite St Columb's cathedral - hence the caption.

Another look-out post

I presume the railings in this one aren't original - probably put there recently to stop local disaffected youths from climbing in and doing some damage.  It looks pretty cramped inside this one - not sure I'd fancy getting in there myself, particularly in the middle of a siege with an angry mob outside throwing all sorts at you.