The First World War cannot be really comprehended, especially by Americans,
until you have driven around France and Belgium and walked through hundreds
of graveyards. The cost in human (and animal) lives is truly staggering.
The mental impact on Europe's countries are still being felt to this day.
As Americans we tend to gather all our combat casualties into one location. Not so the British. They bury their combat dead where they fell so there are small graves all over Europe. From a single grave to tens of thousands at one place. The British did not ship their dead home as a matter of policy. The family could, of course, pay to have them shipped home if they wished.
The Somme Battlefield is one hugh area. There are Memorials all over it. 
Welsh
Memorial in the Somme Battlefield They fought many battles in the area
(and during World War II also during the Fall of France). This Welsh Memorial
is seen from the hilltop just above it looking East.
Rolling
hills of France.Most of the battles of the First World War were fought on
very very flat land. Now flat is a relative term. In Belgium it really is very
flat (we're talking western Belgium of course), but in France the land topography
is is more akin to rolling hills. Some areas have hills that are typically 50
or so feet from trough to crest. As such there areas where the line of sight
is limited so troops behind a hill can be hidden. Hence the need for balloons
and airplanes to scout out troop locations. This area of France shown in this
image has maybe 8 feet of variance. Once of the many reasons an attack "Over
The Top" was so deadly to the soldiers.
Terrain may have started out flat, but after a few hours even the most flat
area would be filled with shell holes. Now this is not always bad. It as
least gave the soldiers someplace to hide.
Vimy
Ridge shell holes. There are some shell holes here that are thirty feet
deep. They used some BIG guns in WWI. Some of the biggest holes are not
from shells, but from mines. All sides would tunnel, place hundreds of
tonnes of explosives beneath the enemy trenches, then blow it up and attack.
Just like what we did during the Civil War outside Richmond. However, the
attacks were usually so poorly planned - - and the orders were followed
to the letter - - that almost every one of them were failures. Seldom did
the mine exploding have the desired effect of blowing a hole in the lines.
This was because the planners had the attack follow anywhere from 5 to
20 minutes after the explosion! The defenders could recover from the shock
and block it.
The British and French Generals rarely got closer to the front closer than 20 miles (35 kilometers). They were totally out of touch of what was going on. British General Haig is a good example of that. His leadership during the Battle of the Somme, in July 1916, wiped out the work Lord Kirtchner did in recruiting the previous year. All the strength the British had built up were gone in three days. 50,000 casualties the first day of which 20,000 were KIA (killed in action). Yet he forced the men to press into the prepared German defenses (their intelligence service knew it was coming).
Vimy
Ridge British Trench The only good success came from the Canadians
who ignored orders and advanced at a run at at the end of the barrage.
They got to the enemy trenches before they could get out and prepare their
defense. They advanced two miles. They also had the lowest casualties
of the day. Any overall advantage the British had were thrown away by
a General who never visited the front.
Steel
protected firing loop in a British Trench. General Haig never really
knew what his men were up against in terrain and combat tactics and never
tried to find out. This is one of the reasons why Field Marshall Montgomery
always had his command vehicles very close to the front lines during the
Second World War. As a Lieutenant on the front he had seen what Generalship
from a Chateau inflicted on the men in the front lines.
Here is a link to two pages of other thumbnail images of French battlefields.