Very clever they were to build those sewres back then with the technology and tools they had available. We rely to much on technology, and when we have to do something manual like that it turns out a complete bodge up. We can't even get a bath fitted straight, let alone god knows how many miles of brick sewer pipes deep under ground. The brick work is amazing, the accuracy is amazing, the whole sewer system is amazing and is still the main system thats in use today all these years on.
When they were digging the first tunnels under the thames, they got a crack in the roof and had to go to the bottom of the thames to fix it. They say that the human waste and human created rubbish at the bottom of the thames was more than six feet deep , lucky he was in a diving suit, what ever they had then.
the sewers wasn't the only thing that are underground though. Williamsons tunnels at liverpool are the work of a true mad man and a pure genious. No one really knows why he paid workers to burrow down and build miles of tunnels interconnecting cellars, rooms, great halls, chambers, and two story underground houses. some say it was just to keep liverpool workers in work, others say he was building an underground city. Most have either been demolished now or are filled with rubbish and ash from bakers shops ovens, but some are being saved, although the government is helping building companies to destroy what is one of this countries greatest wonders.
I've been in some that aren't open to the public, there are cellars, the sub cellars then rooms below that where i was standing on 20+ foot of ash.
If your interested some are open to the public.
Also underground of course is the tube. The tube in london is one of those things like the sewers, but this one people actually go in and think nothing of it. There are many derelict sections of and stations on the tube and some have even had stories written about them- South kentish town by sir john betjemin. Sections of tunnel were built in the war years of these main tube sections as air raid shelters, two floors high, with bunks, but in the end were used for troops mainly. Later becomeing storage areas for government departments. (if you've ever seen the film hidden city it's about secret documents for human chemical warfare experiments being hidden away in these tunnels.)
Then there are of course the secret government tunnels all over the country the ones hidden in hills of train lines and beside motorways. Ever seen those ghost junctions on the motorway that look like they never got built are are there for future development? well one theory is that there's government tunnels near those and that would be the entrance on to the road system for them if needed. Most famous government tunnels are at dover, now a museum.
http://www.williamsontunnels.com/visit.htm
http://www.williamsontunnels.co.uk/view.php?page=about
http://underground-history.co.uk/front.php
http://www.subbrit.org.uk/rsg/featur...ers/index.html
http://www.english-heritage.org.uk/s...onProperty.182
http://www.showcaves.com/english/gb/...ireCorner.html
http://www.londonrailways.net/secret.htm
http://www.fictionalcities.co.uk/tunnels.htm
http://www.southernwater.co.uk/homeA...ours/dates.asp