When it comes to choosing assets to fund your retirement, you don't need to be an actuary or a professional fund manager to know that, you should not put all your eggs in one basket.Property tends to be expensive, so it would inevitably account for a substantial part of a portfolio, but what is needed is a diversified range of investments.An alternative way to give your portfolio a boost would be to look at investing in land.The value of land has risen dramatically in recent years (almost 24% last year) and with the current shortage of affordable housing, the value of land looks set to rise again.This coupled with the fact that good land is seen as a real investment and that supply of this permissible land is always limited - showing why viable plots and sites of land are an attractive investment opportunity.There are no complicated concepts that investors need to understand with land, just that there is an ever-increasing demand for housing and a restricted supply of good plots for sale. Land increases in value in two ways, it goes up in value when property value increases (due to demand outstripping supply) and by land gaining authorisation to have houses built on it.