A typical collapsed core design

Below is an example of a Collapsed Core (Layer 2 access) LAN. Two core switches are used. If high availability is important, each Core does not usually require two Supervisors. Each Core switch has an edge switch connected to it by a single trunk or EtherChannel. An EtherChannel connects the Core switches. This design can be used as a Distribution Block to connect to a larger design with a separate core. Separate buildings dictate that a 3-tier design with a separate Core is used.
For resilience, loops were created. These loops are designed to reduce the possibility of STP issues.
Core switches can be configured for STP Root or HSRP (Odd or Even VLANs on alternative switches). Core switches are capable of inter-VLAN routing. Unnecessary VLANS are removed from trunks.
RootGuard is configured using the downlinks from Core switches. LoopGuard can be configured via inter-Core and uplinks. BPDU Guard and Switchport Host are configured on Edge (end user), Ports