Siege is one of the less popular maps due to its difficulty in escorting the hostages to the rescue zone and that there are very few infiltration routes to take. These pathways include the main route (which contains the outside and the parking lot), the mine, and the sewers. If bots are equipped, they will normally ignore the mines due to their inability to use the elevator switch.
Combat is mainly fierce in the parking lot as this is the only place where it is close to the rooms with the hostages. Snipers are common in this area as they can have take cover behind the stationary vehicles and eliminate targets in the wide open area.
When the Counter-Terrorists have to rescue the hostages, they have to take precautions as the security and bunker rooms are enclosed and the Terrorists will often camp right behind the hostages. For counter-tactics, Flashbangs and Smoke Grenades are used to hamper the enemy's sight and protect team members from most forms of harm.
Even if the Terrorist force was not fully engaged in the parking lot or in the bunker, it is possible for them to retreat and camp nearby the only hostage rescue zone at the main entrance to the parking lot with sniper weaponry or close-ranged weapons.
The Outside consists of a bunker that leads to the sewers (and the mines) and the entrance to the parking lot. For the CTs, the outside is one of the two pathways to take in order to rescue the Hostages. In many situations, this area contains the most intense combat for the first minute of the round.
Automatic weapons and shotguns are not recommended in this section of the map as this wide-open area is more favorable for snipers. Flashbangs are recommended for ambushing, especially if you are attempting to breach through the parking lot as campers are very common. Furthermore, smoke grenades can provide cover and make it harder for enemies to figure out where your team members are moving from a far distance, smoke can provide concealment for your teammate and keep them from picking off by enemy snipers.
While it may be tempting to rush through this area, you need to keep an eye on the bunker which contains a pathway into the mines and the sewers respectively. Sometimes, an enemy player may be camping there and could inflict an ambush that can greatly decrease your team's chance of winning.
The Parking lot contains the second most amount of intense combat, following the outside. Snipers can be quite common although they may only decide to camp in this cramped area if they were forced to retreat or have to retrieve the hostages. In here, shotguns and automatic weapons are highly recommended to counter enemies, especially if they are separated from their team.
Most campers prefer to hide behind the SUV's. To prevent being ambushed by them, be sure to crouch and take a glance below the vehicles. Furthermore, throwing an HE grenade at suspected areas may be tempting but it can easily gain the attention of enemies. Instead, a well displaced Flashbang or a Smoke Grenade is enough to breach through the first line of the opposing team's defense.
If the main entrance is too risky to use, another way is to use the sewers.
Terrorist Spawn Zone/Facility
There are two entryways to the facility. Starting from the parking lot, they are the main door or the vent via a SUV.
Within the security center, there are two rooms that contains two hostages respectively. Note that these rooms contain a visible window that may hamper the Counter-Terrorist's progress as the Terrorists can easily guard the hostages on the other side of the rooms.
Players who use submachine guns or shotguns are at a good advantage due to the enclosed areas. Unless available team members were eliminated and the main objective must be completed before the time runs out, snipers will avoid engaging enemies in this area.
One should remember to always throw an flashbang and stay alert. The automatic doors emit loud noises that announces your arrival, thus making deadly ambushes quite common.
At the lobby, there are possibilities that an ambush could be waiting on the other side of the doors. Due to this, a Smoke grenade can become handy to use. A few player wielding P90, M249 or Galil may blindly spray into the smoke, but generally pop smoke is a safer measure for the attackers. If combined with flashbang after the smoke grenade is out, there is a good chance that defenders will be completely disoriented and they will be easy prey for shotgun users.
The Tactical shield can be effective as well if a user is with their teammates. The former can block some aggressive player's bullets to protect their teammates, and the latter can allow more teammates to come in and destroy the enemy's defense line. However, being alone inside the facility with the shield isn't a good idea.
It may be tempting to hide/camp behind the glass within the security bunker/computer room but it is a very poor choice as you will not have any place to retreat to. Therefore, using the area for cover is not recommended, especially when the enemy is wielding Assault rifles. Unless your weapon are able to penetrate through the glass while enemy's weapon not (the Desert Eagle, Rifles and the M249 can penetrate). This does not apply for Global Offensive however.
Note that the rooms where the hostages are located have vents which allow opponents to throw a flashbang or a smoke grenade and can have enemies swarmed with opposing team members from both sides thus eliminating any chance for retreat. To prevent this, players will be sure to pay attention by observing or patrolling around the facility or simply camp at the room(s) wedged in between the hostage rooms and the computer room.
Similar to cs_militia, there is also an alternative route to reach the hostages if the parking lot and its entrances contain too many players at the beginning of the round. However, be sure to carefully traverse through these areas, especially when you are leaving the sewers since one of the exits leads to the parking lot. Take note that if you are by yourself inside the parking lot, you are very vulnerable to enemy attacks. In conclusion, it is not advised to rush alone to the parking lot.
Fighting almost never occurs here, as players will prefer to guard the hostage rescue zone which is far away from the Counter-Terrorist Spawn Zone. The only main interest of this area is that there is an entrance to the mines which guides players to the elevator of the bunker.
Bots may sometimes fall off the bridge if they attempting to access the mines. However, this is rare as they will normally ignore taking that pathway as they cannot interact with switches.
Fighting is not as intense compared to the other areas as many players will avoid the mines. To many experienced players, using the elevator is too risky as opposing team members can hear the operating elevator and eliminate enemies with ease. Instead, the Counter-Terrorists will rush through the outside as the Terrorists are unlikely to reach that section of the map first.
Note that there is an opening at the top part of the elevator. This can allow enemies to camp above and throw a flashbang to eliminate stunned players. However, if someone activates the elevator, players can be killed if they are caught between the elevator and the roof (This may not happened in 1.6 or earlier version).
Bots will normally never enter through this area as they cannot use the elevator correctly. If they do decide to enter the mines for any reason, the Terrorists may win by default. However, bots will normally ignore the mines due to their inability to use the elevator switch.