Here is my suggestion for a somewhat-less-than-hellish indoor workout:
You'll need a stationary trainer. You can buy a wind trainer that uses a fan for air resistance for less than $100, or you can buy one that uses a rotating magnet that provides adjustable resistance for under $200. Rollers are for the brave, but they do teach smoooooooothness and balance... or else! Some rollers can be had with clamps for the bike's forks, sort of training wheels in reverse....
When you mount the bike in the trainer, place a book beneath the fron wheel, so you won't feel as if you are pedaling downhill. Some companies sell plastic blocks to elevate the front wheel... but I find that a well placed encyclopedia volume works just as well.
Next, pick up one of those electric fans mounted on a pedestal... $25 at any discount department store. Set it up in front of your bike and trainer... the lowest setting will evaporate most of the sweat you will produce, as well as give you a sort-of natural wind-in-the-face experience.
Stock your bike with a couple of water bottles, and have some road snacks within easy reach. Also, have a bath towel nearby... you will sweat, and eventually you will have the rolled up towel draped round your neck. I also wear a bandanna, rolled up and tied as a headband, to prevent sweat from reaching my eyes.
If you set this rig up in your den or salon, you will have a television set nearby. Preferably with a VCR... Rent some videos... road films work best... take some velcro or a few rubber bands and attach the remote control to your handlebars.
Dress in summer bike clothes, minus helmet and glasses. Gloves are optional, but you'll likely shed them after half an hour.
Now, turn down the thermostat, or open some windows... an ambient room temperature of 65 degrees F feels great to me when I ride indoors (but tends to make the other household members complain.)
Turn on the fan, mount the bike, beging riding, watch a video. Two hours of this is not such a bad way to pass a freezing or raining Saturday morning, and when you dismount and wobble away to the shower, you will feel as if you've accomplished something. I find that I ride much faster... sustained speed... when I ride indoors, and my muscles feel the difference.
A few things to note: I use an old bike when riding indoors. Sweat will corrode the bike, no matter how careful I am. For years, I used a wrecked Fuji Sagres tourer as a trainer... both the top and the down tube were bent at the headstock, and the fork was bent enough to allow the fron wheel to contact the frame. (After an altercation with a furniture truck.) This did not prevent the bike from being a perfect indoor trainer...
I have computers on all of my bikes... I'm a statistic junkie, and I keep track of my mileage and general performance. For trainer work, I mount the magnet on the rear wheel, and the Hall Effect Sensor on the seatstay... One can buy rear wheel mounts for bike computers, but I just splice in a length of shielded wire (Old Walkman headset wire works very well.)
Also, rear tires wear out very rapidly from contact with the hard, small diameter roller. A thousand indoor miles will render a tire unsafe for real road or trail use, so mount an old back tire before you ever begin. If you have a mountain bike, mount a smooth rear tire... otherwise you'll awaken the dead with a sawmill-like roar from a knobbly rear tire. Make sure that the tension is set right between the tire and roller... Too tight, and you'll strain to turn the pedals, too loose and the tire will slip against the roller... and heat up... and possibly explode with a shotgun like BANG! (As happenned to me early on.)
I don't worry about heart rate, training programs, intervals or sprints... I just concentrate on smooth, fast pedaling, I try to prevent the rig from rocking side to side, and generally have a time or mileage goal for the session.
Plus, I stay caught up with the latest rental videos...