\usepackage {colortbl}
\setlength{\extrarowheight}{2mm}
\begin{tabular}{|l|c|c|c|c|c|c|c|}
\hline
Sydney    & OG4G &Thu Oct 10 &Mon Oct 21 or 28 &11 or 18 days &999\\
\rowcolor[gray]{0.5}
          &      &Thu Oct 17 &Mon Oct 21 or 28 & 4 or 11 days &999\\
          &OG7A  &Sun Oct 13 &Mon Oct 21 or 28 & 8 or 15 days &999\\
\rowcolor[gray]{0.5}
          &      &Sun Oct 20 &Mon Oct 28       & 8 days       &999\\
\hline
\end{tabular}