The Atlas detector is much bigger than earlier detectors like the Opal in the LEP accelerator. It is approximately 22 m high and 44m long. The view of the Atlas detector in comparison to a human can be found here.
This animation shows the fundamental construction of the detector.

The presentation of the events in the Atlas detector is shown with the help of the Hypatia program. You can try it out here

Hypatia is an interactive laboratory environment for particle collisions. Here you can study events recorded in proton-proton collisions with the Atlas detector at the Large Hadron Collider (LHC). The events in the Atlas detector can be displayed in end- and side-views. With the mouse you can zoom in and out. In contradiction to Wired all subdetectors are always visible. In proton-proton collisions at those large energies many more particles are generated than in electron-positron collisions at LEP. Thus, you can often find many more tracks than in the Opal experiment. Individual tracks can be chosen separately with the pick tool. Also, you can suppress tracks below a certain energy threshold transverse to the incoming beams.
The program has multiple windows which we now look on seperately. The first one is the Track Momenta Window:

The Track Momenta Window shows the different particle tracks in the detector. In the upper bar you find buttons to get to the previous or the next event. With File→Animated Event you can see the event in motion.

The entry Show simulated is not necessary and should not be checked.

After the name of the event file you see the missing energy ETMis in GeV which is a result of non detectable particles (i.e. neutrinos) or measurement mistakes.

The table shows from left to right track number, the energy of the particle, its charge, the transversal energy (the energy perpendicular to the direction of the incoming proton beams) and the angle of the track (the original particle beams are in z direction and you see the x-y plane in the Canvas Window, described on the next page).

If you click on a row, you see the associated tracks in the Canvas Window.

The Canvas Window shows a picture of the selected event. The tracks of the charged particles are shown as lines in the tracking detectors. Neutral particles, like the photon, do not leave any tracks. Both deposit energy in the calorimeters.

The event can be viewed from the side(Side-View) and along the incoming beams(End-View). The dashed line in the front view shows the direction of the missing energy caused by undetected particles (e.g. neutrinos) or mismeasured energies. Holding and moving the cursor in the window will zoom in or out.

Checking the pick mode single tracks in the tracking detectors can be selected by mouse click and their information in the Track Momenta Window will be highlighted.

Please note, that outside of the outermost ring the total energy deposition in the calorimeters is denoted.

Now we look at the Control Window:

In this window you can toggle between end- and side-view in Projection. Selecting Zoom you can zoom with the mouse in the canvas window and with Pick you select individual tracks which will be highlighted in the picture and in the table.

With the help of Cut you can suppress all tracks below a certain threshold of transverse energy, i.e. energy carried away perpendicular to the incoming beams.

Now you know how both detectors are constructed. Click now to start Challenge1.

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