In late October and early November 2003 a series of some of the most powerful solar eruptions ever registered shook the heliosphere. These “Halloween storms” damaged 28 satellites, knocking two out of commission, diverted airplane routes, and caused power failures in Sweden, among other problems. This paper presents a 4-day end-to-end simulation of one of the major events (following the X17 flare) that produced the most geoeffective interval of the Halloween storm. The simulation was carried out with the newly developed Space Weather Modeling Framework (SWMF, see http://csem.engin.umich.edu/SWMF) that self-consistently couples physical domain models spanning from the solar corona to the upper atmosphere. The various attempts and iterations leading to the final simulation are also described. We briefly discuss the technological advances enabling the faster than real-time operation of the SWMF with the required high resolution. We compare the simulation results with observations from space- and ground-based measurements. We have also performed a reference magnetospheric simulation driven by ACE and Geotail observations and compared its results with the Sun-to-thermosphere simulation and the magnetospheric observations. The magnetic structure of the coronal mass ejection (CME) observed at the L1 point on the ACE spacecraft is not correctly reproduced because of the insufficient observations and theoretical understanding of the CME initiation mechanism. On the other hand, we find that the SWMF reasonably well reproduced both the hydrodynamic characteristics of the coronal mass ejection and some of the major indexes characterizing the strength of the geomagnetic storms.