Last year I tried to make the 3 weeks meaningful by spending some time each day imagining being in Jerusalem as the Romans breached the walls. This picture was heavily influenced by the Avalon Hill war game Siege of Jerusalem. In the game, the first time any Roman unit enters an area of Jerusalem the Roman's haven't been in previously, they are immediate attacked by random inhabitants - people with knives, clubs and other improvised weaponry. By the rules, these people are effectively committing suicide - the best outcome of the combat for them against an intact legion unit is that they are not destroyed and do minimal damage to the unit. But that image of the people of Jerusalem swarming from the surroundings like dragon's teeth with toothaches stayed with me. I also tried to visualize being one of the Cohanim - as day after day rolled by without being able to offer the daily tamid and the increasing fear that this time Hashem wasn't going to send a plague to strike down the besiegers as He did Sanchirev.
This year instead I'm trying to make myself feel the absence of the Beit Hamikdash. To know that once there was a place where Hashem was undeniably manifest, but now it is gone. To visualize the daily activity as the kohanim, leviim and yisraelim performed their daily functions.
In my vision today, a man comes to offer a todah (thanksgiving offering) for a child who miraculously survived an illness. As designed, the todah offering is too large for even an entire family to eat, so they and their neighbors have an informal block party, eating the sacrifice, singing tehillim (psalms) of praise and gratitude, and feeling a direct connection to Hashem that Larry in the 21st century finds almost unimaginable. They have two days and the intervening night to finish eating the sacrifice, so the child's grandparents are able to come from their farm outside Jerusalem to join the celebration. They bring their ma'aser sheni money and buy some extra supplies for the celebration - perhaps some olives soaked in a salty brine so as to consume one of the 7 foods for which the land of Israel is praised.
That's all gone now - I've only ever been to one seudat hodah. It was moving, but isn't the same when it is ordinary food and not kodoshim (holy food).